THE  LIBRARY 

OF 

THE  UNIVERSITY 
OF  CALIFORNIA 

GIFT  OF 
William  K.  Mitchell 


TO   TEACHERS  AND   OTHERS. 


Sfust  $tt&U$cfc,  anfc  for  Sale  &» 

JOHX  GRIGG, 

No.  9,  North  Fourth  Street,  Philadelphia, 

AND    FOR  SALS   BY  BOOKSELLERS    AND  COUNTRY    MERCHANTS    GENERALLY 
IN   THE    SOUTHERN   AND   WESTERN    STATES, 

TORREY'S  PRIMER,  or  First  Book  for  Children. 

TORREY'S  SPELLING  BOOK,  or  Second  Book  for  Children. 

Those  Teachers  who  are  not  altogether  prejudiced  in  favour  of  Webster,  will  please  examine 
this  work ;  as  numerous  Preceptors,  who  have  used  it  in  their  Schools,  give  it  the  preference 
oror  that  and  others. 

TORREY'S  PLEASING  COMPANION  FOR  LITTLE  GIRLS  AND  BOYS,  blending 
.  Instruction  with  Amusement ;  being  a  Selection  of  Interesting  Stories,  Dialogues,  Fables,  and 
Poetry.  Designed  for  the  use  of  Primary  Schools  and  Domestic  Nurseries. 

Preferred  generally  to  Murray's  Introduction,  and  works  of  that  class,  by  Teacher^  who  have 
given  it  an  examination. 

TORREY'S  MORAL  INSTRUCTOR,  OR  GUIDE  TO  VIRTUE.— Letters  of  decided 
approbation,  from  several  of  the  most  eminent  statesmen  and  heads  of  colleges,  academies  and 
schools,  might  be  added  in  favour  of  these  books:  but  the  compiler,  in  preference,  earnestly 
requests  that  teachers,  parents,  merchants  and  others,  will  examine  for  themselves  as  soon  as 
practicable ;  and  in  proportion  as  this  is  done,  he  indulges  the  belief  (from  experience)  that 
they  will  be  generally  introduced  into  schools  and  families  throughout  the  United  States;  and 
that  consequent  to  this,  the  intellectual  and  moral  improvement  and  virtue  of  the  present  and 


This  and  the  preceding  works  have  been  generally  introduced  in  schools  and  academies  in 
place  of  Murray's  Reader,  and  other  similar  works  of  domestic  and  foreign  origin.  It  has 
been  the  special  endeavour  of  the  compiler,  besides  adapting  the  lessons  in  his  books  progres- 
sively to  the  age  and  capacities  of  the  learner,  to  combine  entertainment  with  useful  instruc- 
tion. He  has  inserted  a  considerable  number  of  lessons,  designed  to  impress  the  mind  of  the 
rising  generation  with  a  just  abhorrence  of  the  prevailing  custom  of  using  ardent  spirits,  which 
is  probably  the  most  destructive  and  extensive  moral  and  physical  evil  that  ravages  our 
Republic  at  the  present  time. 

"  Dr.  Torrey's  works  abound  with  admirable  Lessons,  in  moral  and  physical  knowledge, 
which  the  old  as  well  as  the  young  may  read,  with  pleasure  and  profit.  The  best  feelings  of 
our  nature  are  encouraged  and  cultivated,  the  purest  principles  of  morality  are  made  plain 
and  attractive  to  the  youthful  understanding,  and  every  thing  is  explained  with  so  much 
simplicity  and  perspicuity,  that  every  reader  may  comprehend  them." 

SMILEY'S  ARITHMETICAL  RULES  AND  TABLES  FOR  YOUNG  BEGINNERS. 
This  is  the  best  work  of  the  kind  now  in  print;  but  Teachers  are  particularly  reo nested  to 
examine  for  themselves. 

SMILEY'S  ARITHMETIC,  or  the  New  Federal  Calculator,  in  dollars  and  cents.  This 
work  contains,  among  other  important  improvements,  Questions  on  the  Rules  and  Theory  of 
\rithmetic,  which  are  considered  by  Teachers  generally,  very  conducive  to  the  improvement 

Although  a  prejudice  exists  among  some  Teachers  in  favour  of  the  old  works  on  Arithmetic, 
yet  the  very  liberal  patronage  which  this  work  has  received,  must  be  considered  as  decisive 
evidence  of  the  great  estimation  in  which  it  is  held  by  most  of  the  instructors  of  youth. 
Upwards  of  50,000  copies  have  been  printed  and  sold.  The  sums  being  altogether  in  dollars 
and  cents,  gives  it  a  decided  preference  over  any  other  Arithmetic  in  use.  The  most  distiri- 
(fuiohed  Teachers  of  our  city  pronounce  it  superior  to  any  other  like  work ;  therefore  the 
imbhsher  sincerei;  hopes  this  useful  improvement  vill  overcome  the  prejudice  that  many 


I 


2  JOHN  GRIGG'S  SCHOOL  BOOKS. 

Teachers  have  to  introducing  new  works ;  particularly  those  preceptors  who  wish  to  discharge 
their  ducy  faithfully  to  parent  and  child. 

Among  the  numerous  flattering  testimonials  of  its  superiority  over  any  other  now  in  use,  ia 
the  following,  from  gentlemen  who  enjoy  well-merited  celebrity  as  instructors  of  youth  in  our 
city,  as  well  as  in  the  New  England  States.  "  Philadelphia,  Sept.  18,  1829.— We  have  ex- 
amined with  care  and  attention  the  '  New  Federal  Calculator,  or  Scholar's  Assistant,'  by 
Thomas  T.  Smiley ;  and  have  no  hesitation  in  pronouncing  it  an  excellent  Arithmetic.  Tho 
arrangement  is  good,  and  has  evidently  resulted  from  the  reflections  of  a  practical  and  judi 
cious  Teacher;  the  definitions  and  rules  are  expressed  in  clear  and  simple  language,  well 
adapted  to  the  capacities  of  the  young;  the  questions  are  convenient  for  the  purpose  of  ex 
animation;  the  examples  of  a  strictly  practical  character;  and  the  book  on  the  whole  i» 
admirably  calculated  for  the  use  of  schools  and  academies.  John  M.  Brewer,  John  Frost, 
S.  C.  Walker." 

The  editors  of  the  New  York  Telegraph,  speaking  of  Smiley's  Arithmetic,  observe,  "  We 
do  not  hesitate  to  pronounce  it  an  improvement  upon  every  work  of  that  kind  previously 
before  the  public,  and  as  such  recommend  its  adoption  in  all  our  schools  and  academies." 

A  KEY  TO  THE  ABOVE  ARITHMETIC;  in  which  all  the  examples  necessary  for  a 
Learner  are  wrought  at  large,  and  also  Solutions  given  of  all  the  various  Rules.  Designed 
principally  to  facilitate  the  labour  of  Teachers,  and  assist  such  as  have  not  the  opportunity  ol 
a  Tutor's  aid.  By  T.  T.  Smiley,  Author  of  the  New  Federal  Calculator,  &c.  &x. 

SMILEY'S  EASY  INTRODUCTION  TO  THE  STUDY  OF  GEOGRAPHY,  on  an 

improved  plan ;  compiled  for  the  use  of  Schools,  with  a  view  to  render  the  acquisition  of 
Geographical  Science  easy  and  pleasant  to  the  Student:  accompanied  by  an  Atlas,  engraved 
under  the  superintendance  of  H.  S.  Tanner,  Esq.  and  T.  T.  Smiley,  improved  to  the  present 
time ;  exhibiting  the  Elevation  of  Mountains,  Length  of  Rivers,  and  Population  of  Cities,  &c. 
&c.  from  the  best  authorities. 

When  we  say  this  is  the  best  Elementary  Geography  and  Atlas  in  use,  we  only  reiterate  the 
sentiments  of  many  of  the  most  distinguished  teachers  in  our  country.  The  work  is  particularly 
adapted  for  Schools  and  Academies,  and  Teachers  who  are  anxious  to  promote  one  of  th» 
most  -useful  and  agreeable  studies,  will  please  give  it  an  attentive  examination. 

GRIMSHAW'S  HISTORY  OF  THE  UNITED  STATES. 

Also,  Questions  adapted  to  the  above  History;  and  a  Key,  adapted  to  the  Questions,  for  the 
ase  of  Teachers,  and  Private  Families. 

GRIMSHAW'S  HISTORY  OF  ENGLAND. 

Also,  Questions  adapted  to  the  above  History;  and  a  Key,  adapted  to  the  Questions,  for  the 
use  of  Teachers,  and  Private  Families. 

GRIMSHAW'S  IMPROVED  EDITION  OF  GOLDSMITH'S  HISTORY  OF  GREECE, 
with  a  Vocabulary  of  the  Proper  Names  contained  in  the  work,  and  the  Prosodial  Accents,  in 
conformity  with  the  pronunciation  of  Lempriere. 

Also,  Questions  adapted  to  the  above  History;  and  a  Key,  adapted  to  the  Questions,  for  the 
use  of  Teachers,  and  Private  Families. 

GRIMSHAW'S  IMPROVED  EDITION  OF  GOLDSMITH'S  HISTORY  OF  ROME, 
revised  and  corrected,  and  a  Vocabulary  of  Proper  Names  appended,  with  Prosoxiial  Marks 
to  assist  in  their  pronunciation. 

Also,  Questions  adapted  to  the  above  History;  and  a  Key,  adapted  to  the  Questions,  for  the 
use  of  Teachers,  and  Private  Families. 

The  Editor  of  the  North  American  Review,  speaking  of  those  Histories  observes,  that— 

~"  remember  to  have  seen 
of  the  United  States,' 

^ r ear  1821.    It  is  a  small 

volume,  and  a  great  deal  of  matter  is  brought  into  a  narrow  space"; — but  the  Author  has 
succeeded  so  well  in  the  construction  of  his  periods,  and  the  arrangement  of  his  materials, 
that  perspicuity  is  rarely  sacrificed  to  brevity. 

"The  chain  of  narrative  is  skilfully  preserved,  and  the  Author's  reflections  are  frequently 
such  as  make  the  facts  mote  impressive,  and  lead  the  youthful  mind  to  observe  causes  and 
consequences  which  might  otherwise  hare  been  overlooked.  As  a  School  Book  it  may 
justly  be  recommended. 

"  What  has  been  said  of  this  volume  will  apply  generally  to  his  other  historical  works.— 
They  are  each  nearly  of  the  same  size  as  the  one  just  noticed,  and  designed  for  the  same 
object,  that  is,  the  use  of  Classes  in  Schools. 

"The  '  History  of  England,  is  an  original  composition;  but  the  Grecian  and  Roman  Histo- 
ries are  Goldsmith's,  improved  by  Mr.  Grimshaw,  in  which  he  has  corrected  the  typographical 
errors,  with  which  the  later  editions  of  Goldsmith's  Abridgments  so  much  abound ;  and 
removed  any  grossness  in  language,  which,  in  some  few  instances,  rendered  these  valuable 
•ompends  less  useful  in  the  Schools  to  which  Youth  of  both  sexes  resort.  He  has  also  added 
a  Vocabulary  of  proper  names  accentuated,  in  order  to  show  their  right  pronunciation,  which 
is  a  valuable  appendage  to  the  History. 


•*£-. 


NEW 

CONVERSATIONS  ON  CHEMISTRY, 


ADAPTED  TO  THE 


PRESENT  STATE  OP  THAT  SCIENCE; 


ITS  ELEMENTS  ARE  CLEARLY  AND  FAMILIARLY  EXPLAINED,      d 

WITH 

ONE  HUNDRED  AND  EIGHTEEN  ENGRAVINGS  ILLUSTRATIVE 

OF  THE  SUBJECT  J   APPROPRIATE  QUESTIONS  J   A 

LIST  OF  EXPERIMENTS,  AND  A  GLOSSARY. 


ON  THE  FOUNDATION  OP 

MRS.  MARCET'S  "CONVERSATIONS  ON  CHEMISTRY." 


BY  THOMAS  P.  JONES,  M.  D. 

Professor  of  Chemistry  in  the  Medical  Department  of  th«  Columbian  College, 
Washington  City. 


JOHN  GRIGG,  No.  9  NORTH  FOURTH  STREET. 

•1832. 


For  Sale  also  by  the  same  Publisher, 

CONVERSATIONS  ON  NATURAL  PHILOSOPHY,  in  which  the 
Elements  of  that  Science  are  familiarly  explained.  Illustrated  with  Plates. 
By  the  Author  of  Conversations  on  Chemistry,  &e.  With  Corrections, 
Improvements,  and  Considerable  Additions  in  the  hody  of  the  Work  ; 
.Appropriate  Questions,  and  a  Glossary.  By  Dr  THOMAS  P.  JONES,  Author 
of  the  New  Conversations  on  Chemistry.  In  1  vol.  12mo. 


iQAN  STACK 


GIFT 


Entered  according  to  the  Act  of  Congress,  in  the  year  eighteen  hundred  and 
thirty-one,  by  John  Grigg,  in  the  Clerk's  Office  of  the  District  Court  of  the 
Eastern  District  of  Pennsylvania. 

•'     •    .  7W 


PREFACE. 


The  CONVERSATIONS  ON  CHEMISTRY,  written  by  Mrs  Marcet,  have 
acquired  and  sustained  a  deservedly  high  reputation,  and  have  un- 
doubtedly, contributed  more  than  any  other  work  to  promote  the  study 
of  chemistry  as  a  popular  branch  of  education.  The  writer  of  the  fol- 
lowing pages  is  not  so  sanguine  as  to  hope  that  his  labours  will  obtain 
for  him  so  rich  a  reward,  although,  in  executing  the  task  which  he  has 
undertaken,  his  principal  motive  has  been  to  facilitate  the  acquisition 
of  knowledge  in  a  branch  of  science  to  which  he  has  paid  much  atten- 
tion, and  of  which  he  has  for  many  years  been  a  zealous,  and,  he 
believes,  a  successful  teacher. 

Some  time  since,  he  edited  a  revised  edition  of  the  CONVERSATIONS  ON 
NATURAL  PHILOSOPHY,  by  the  same  author,  and  was  engaged  to  per- 
form a  similar  task  with  those  on  chemistry.  After  passing  over  a  few 
pages  with  this  design,  he  found  that  it  would  be  more  difficult  to  adapt 
the  work  to  the  present  state  of  the  science  than  to  remodel  it  alto- 
gether. Upon  a  careful  comparison  of  the  two  works,  it  will  be  found, 
therefore,  that  although  a  few  pages  of  the  original  have  been  retained, 
with  but  slight  alterations,  the  conversations  are,  in  general,  entirely 
new. 

About  twenty-five  years  have  elapsed  since  the  CONVERSATIONS  ON 
CHEMISTRY  were  first  published ;  and  in  a  department  of  science  so 
progressive  as  that  to  which  they  relate,  advances  have  been  made 
during  this  interval  which  have  affected  it  in  nearly  all  its  branches. 
Many  judicious  alterations,  it  is  true,  have  been  made  in  the  succes- 
sive editions  of  the  work;  but  still  the  original  platform  has  remained 
unchanged,  although  some  of  the  supports  upon  which  it  rested 
have  given  way  with  the  lapse  of  time. 

The  CONVERSATIONS  ON  CHEMISTRY  were  undoubtedly  intended  as  a 
companion  for  the  parlour,  and  they  were  admirably  adapted  to  the  end 
proposed.  The  many  excellencies  of  the  work,  however,  have  caused  it 
to  be  extensively  adopted  for  the  use  of  classes  in  schools  ;  but  its  em- 
ployment in  this  way  has  been  accompanied  by  many  difficulties,  as 
those  colloquial  digressions  which  gave  variety  and  interest  to  it  in  the 
family  circle,  were  altogether  unsuited  to  the  business  of  the  school 
room.  Whilst,  in  the  following  work,  an  attempt  has  been  made  to 
imitate  the  style,  and  to  preserve  some  of  those  interesting  traits  which 
rendered  the  original  work  so  acceptable  to  every  person  of  taste,  the 
object  in  view  has  imposed  some  sacrifice  in  these  particulars.  A 
much  greater  number  of  facts  have  been  embraced  within  the  same 
space,  and  it  is  hoped  that  the  sacrifice  which  was  unavoidable  under 
the  particular  yiews  of  the  writer,  will  not  be  unattended  by  those  ad- 
vantages which-it  has  been  his  object  to  attain. 


ir  PREFACE. 

It  may  be  thought  by  some  persons  that  several  of  the  conversations 
contain  matter  too  abstruse  for  an  elementary  work.  After  much  con- 
sideration upon  the  subject,  the  author  has  arrived  at  a  different  con- 
clusion. Although  a  judicious  teacher  may  think  it  wise,  in  the  first 
instance,  to  omit  some  of  the  conversations,  either  in  whole  or  in  part, 
the  matter  contained  in  them  will  not  vitiate  the  other  portions  of  the 
work,  and  may  be  advantageously  included  in  a  re-examination  of  the 
subject. 

The  numbers  which  refer  to  the  questions  will  be  found  of  great  ad- 
vantage in  directing  the  pupil  to  the  subject  matter  of  inquiry.  The 
list  of  experiments  has  been  confined  to  those  which  are  used  as  illus- 
trations in  the  work;  and  where  it  has  been  thought  necessary,  some 
additional  instructions  have  been  given  for  the  performance  of  them. 
The  Glossary  has  been  introduced  for  the  purpose  of  explaining  a  few 
terms,  and  introducing  certain  facts,  which  could  be  most  conveniently 
placed  there.  It  was  thought  altogether  unnecessary  to  extend  it  fur- 
ther;  as,  in  most  instances,  the  general  index  will  furnish  the  means 
of  obtaining  a  more  satisfactory  explanation  of  the  language  of  chemis- 
try, than  could  be  afforded  by  a  mere  glossary. 


CONTENTS. 

CONVERSATION  I. 

OK  THE  GENERAL  PRINCIPLES  OF  CHEMISTRY. 

Intimate  connexion  of  Chemistry  and  Mechanical  Philosophy.  Chemis- 
try as  a  Science  and  as  an  Art.  Ancient  and  Modern  Chemistry. 
Difference  between  Mechanical  and  Chemical  Action.  Definition  of 
Chemistry.  Simple  and  Compound  Bodies.  Analysis  and  Synthe- 
sis. Chemical  Attraction.  Affinity,  or  Elective  Attraction.  13 

CONVERSATION  H. 

ON  IMPONDERABLE  AGENTS. 

Chemical  Agents  divided  into  Ponderable  and  Imponderable.  Light  and 
Heat  capable  of  separation.  Chemical  effects  of  Light.  Combination 
•with compound  bodies.  Phosphorescence.  Caloric.  Heat,  its  sour- 
ces, Free  and  combined  Caloric.  Tendency  of  heat  to  Equilibrium. 
Slow  Communication  and  Radiation.  Good  and  bad  Conductors.  23 

CONVERSATION  III. 

FREE  CALORIC  CONTINUED. 

Difference  in  the  Conducting  Power  of  Bodies.  Fluids  the  worst  Conduc- 
tors. Radiation  of  Caloric.  Pictet's  Experiments.  Radiating  power 
of  different  surfaces.  Power  of  absorbing  different  in  different  surfa- 
ces. Distinction  between  Radiation  and  Reflection.  33 

CONVERSATION  IV. 

ON  THE  EFFECTS  OF  CALORIC. 

Dilatation  of  Bodies.  Pyrometer.  Thermometer.  Fixed  Points.  Air 
Thermometer.  Differential  Thermometer.  Exceptions  to  the  Law 
of  Expansion.  Fusion  or  Liquefaction.  43 

CONVERSATION  V. 

EFFECTS  OF  CALORIC  CONTINUED. 

Fixed  and  volatile  Bodies.     Evaporation  and  Vaporization.     Boiling. 
A  2 


vi  CONTENTS. 

Influence  of  Atmospheric  Pressure.  Steam.  Solution  and  Saturation. 
Wollaston's  Thermometer.  Water  frozen  by  vaporizing  ether. 
Distillation.  Ignition.  54 

CONVERSATION  VI. 

OS  COMBINED  CALORIC,  COMPREHENDING  SPECIFIC  AND  LATENT  HEAT. 

Bodies  have  different  Capacities  for  Heat.  Proof  by  different  Metals. 
Mercury  and  Water  compared.  Rarefaction  and  Condensation, 
Distinction  between  Specific  and  Latent  Heat.  Change  of  Form. 
Mixture  of  heated  Water  and  Ice.  Heat  latent  in  Steam  and  Vapour. 
Condensation  of  Steam.  Snow  and  Salt  as  a  freezing  Mixture.  65 

CONVERSATION  VII. 

LATENT  HEAT  CONTINUED. 

Heat  rendered  sensible  by  Solidification.  Freezing  by  Evaporation  and 
by  Mixture.  Natural  Temperature,  how  equalized.  Dew.  Hoar 
Frost.  Clouds.  Fogs.  Rain.  /Snow.  Hail.  Causes  of  Cold  at 
great  Heights.  76 

CONVERSATION  VIII. 

ON  ELECTRICITY. 

Name.  Appearances  produced  by  Friction.  Opinions  respecting  its 
Nature.  Analogy  with  Heat.  Positive  and  Negative.  Theory  of  a 
single  and  of  tAvo  Fluids.  Electrical  Machine.  Conductors  and  Non- 
conductors. Spark  and  Shock.  LeydenJar.  Insulation.  Induction. 
Franklinian  theory  of  the  Leyden  Jar.  Lightning  and  Thunder.  86 


CONVERSATION  IX. 

ON  VOLTAIC  ELECTRICITY,  OR  GALVANISM. 

Discoveries  of  Galvani.  Discoveries  of  Volta.  Pile,  Trough,  and  Cou- 
ronne  des  tasses.  Motors  of  Electricity.  Action  of  Acids  on  Metals, 
applied  to  the  Trough.  Opinions  of  Volta,  Wollaston  and  Davy. 
Dr  Hare's  views.  Calorimotor.  Electro-Magnetism.  Thermo- 
Magnetism.  95 

CONVERSATION  X. 

ON  ATMOSPHERIC  AIR,  OXYGEN,  NITROGEN,  OR  AZOTE,  AND  COMBUSTION. 

Constitution  of  Atmospheric  Air.  Simple  Gases.  Vapours.  Distinc- 
tive Properties  of  Oxygen  and  Nitrogen.  Combustion  of  a  Candle  in 
Atmospheric  Air.  Lavoisierian  Theory  of  Combustion.  Its  defects. 
Fixed  and  Volatile  Products.  Oxygen  discovered  by  Priestley.  How 
obtained.  Pneumatic  Cistern.  106 


CONTENTS.  Vii 

CONVERSATION  XI. 

ON  OXYGKW,  SOME  OF  ITS  COMBINATIONS,  AND  THE  NAMES  GIVEN  TO  THEM. 

Combustion  of  a  Candle.     Of  Iron  Wire.    Oxides  and  Oxidation.     Acids        , 
and  Alkalies.     Names  of  Acids.     Tests  or  Reagents.     Decomposi- 
tion of  the  Alkalies.     Neutralization.     Nomenclature  of  Oxides.     Of 
Salts  and  their  Bases.     Designation  of  Combining  Proportionals.         113 

CONVERSATION  XII. 

ON  HYDROGEN,  AND  ITS  COMBINATIONS  WITH  OXYGEN. 

Water  a  Compound  Substance.  Conjecture  of  Sir  Isaac  Newton.  In- 
flammable Air.  Natural  Sources  of  Hydrogen.  Formation  of  Water. 
Hydrogen  always  obtained  from  this  Fluid.  Processes  by  which 
Hydrogen  is  obtained.  Used  for  filling  Air  Balloons.  Proofs  of  its 
Levity.  Explodes  with  Oxygen.  Proportionate  quantities  of  each. 
Discovery  of  the  Composition  of  Water.  Large  quantky  formed  by 
the  French  Chemists.  Musical  Tones  in  Glass  Tubes.  Soap  Bub- 
bles filled  with  Hydrogen  alone  and  in  mixture.  Some  properties  of 
Water.  Deutoxide  of  Hydrogen.  121 

CONVERSATION  XIII. 

ON  SULPHUR  AND  ITS  COMBINATIONS  WITH  OXYGEN  AND  HYDROGEN. 

Properties  of  the  Non-metallic  Simple  Inflammables.  Natural  History 
of  Sulphur.  Sublimation.  Combustion  of  Sulphur  in  Atmospheric 
Air.  Acid  formed  by  its  Combustion.  Absorption  of  Gases  by  Wa- 
ter. Their  Liquefaction.  Bleaching.  Manufacture  of  Sulphuric 
Acid.  Sulphuretted  Hydrogen.  Harrowgate  Waters.  Hydrosul- 
phurets.  135 

CONVERSATION  XIV. 

ON  PHOSPHORUS,  AND  SOME  OF  ITS  COMBINATIONS. 

Discovery  of  Phosphorus.  Substances  in  which  it  is  contained.  Its 
Combustion.  Phosphoric  and  Phosphorous  Acids.  Phosphuretted 
Hydrogen.  Nascent  State  of  a  Gas.  Phosphuret  of  Lime.  Modes 
of  procuring  Phosphuretted  Hydrogen.  Eudioraetry  and  Eudiome- 
ters. Application  of  Phosphorus  and  of  Hydrogen  to  Eudiometry.  142 

CONVERSATION  XV. 

ON  CARBON  AND  ITS  COMBINATIONS  WITH  OXYGEN  AND  HYDROGEN. 

Method  of  obtaining  pure  Charcoal.  Common  Method  of  making  it. 
Diamond.  Newton's  Conjecture.  Insufficiency  of  Art  to  imitate 
many  Natural  Productions.  Charcoal  indestructible  by  Time,  and 
by  Heat.  Antiseptic.  Absorbs  Gases.  Carbonic  Acid.  Soda  Wa- 
ter. „  Carbonates.  Gaseous  Oxide  of  Carbon.  Carburetted  Hydro- 


viii  CONTENTS. 

x 

gen.     Obtained  from  Ponds.     Heavy  Carburetted  Hydrogen,  or  Ole- 
fiant  Gas.     Davy's  Safety  Lamp.      Naphtha.  150 


CONVERSATION  XVI. 

ON  THE  ALKALIES. 

Distinguishing  Characters  of  the  Alkalies.  Fixed  and  Volatile  Alkalies. 
Potassa.  Soda.  Formation  of  Soap.  Caustic  and  Mild  Alkalies. 
Ammonia.  Sal  Ammoniac.  Liquid  Ammonia.  Formation  of  Am- 
monia by  the  decomposition  of  Animal  Matter.  Carbonate  of  Am- 
monia. 


CONVERSATION  XVH. 

OIT    TEE    EARTHS    AND    SOME    OF   THEIR  COMBINATIONS,    AND    ON    METEORIC 

STONES. 

Alkaline  Earths.  Lime.  Quicklime.  Slaked  Lime.  Lime-water. 
Carbonate  and  Sulphate  of  Lime.  Lime  as  a  Manure.  Calcium. 
Baryta,  or  Barytes.  Strontia.  Barium  and  Strontium.  Magnesia. 
Carbonate  and  Sulphate  of  Magnesia.  Magnesium.  Silex.  Glass. 
Vitrification  of  Earths.  Enamels.  Silicon.  Alumina,  or  Argil. 
Pottery.  Earthenware  and  Porcelain.  Aluminum.  Zirconia. 
Glucina,  Yttria  and  Thorina.  Meteoric  Stones.  172 


CONVERSATION  XVHI. 

ON  THE  METALS  IN  GENERAL. 

Number  of  Metals  known.  Their  distinguishing  Characteristics.  Ores 
and  native  Metals.  Roasting,  Smelting,  and  general  process  of  Re- 
duction. Oxidation  and  Reduction  of  the  perfect  Metals.  Oxidation 
and  Solution  by  Acids,  with  the  formation  of  Salts.  Nomenclature 
of  Metallic  Oxides.  Alloys  of  Metals.  Malleability  and  Ductility. 
Soldering.  Welding.  Combustibility  of  Metals.  Gas  holder. 
Hare's  Oxy-hydrogen,  or  Compound  Blowpipe.  Combustion,  Fu- 
sion, and  Ignition  produced  by  it.  Modification  of  the  Blowpipe,  by 
condensing  the  Gases.  Metallic  Sulphurets  formed  with  Extrica- 
tion of  Light  and  Heat. 

CONVERSATION  XIX. 

ON  THE  PARTICULAR  METALS. 

Metals  known  to  the  Ancients.  Those  which  have  been  discovered 
since  the  15th  century.  Gold,  its  mines,  modes  of  gilding  with,  and 
its  general  properties.  Platinum,  its  properties,  and  the  ignition  of 
Spongy  Platinum  by  Hydrogen.  Metals  contained  in  the  ore  of 
Platinum.  Silver,  Nitrate,  and  Fulminate  of  Silver,  and  other  Ful- 
minates. Cinnabar,  Mercury,  its  Uses  and  Properties.  Iron,  Cast 
Iron,  Steel,  and  Plumbago.  Magnetic  Property  of  Iron  and  oth<y 
Metals.  Copper,  its  Uses  and  Combinations.  Lead,  its  Oxides, 
and  other  Combinations.  Tin,  its  Alloys  and  Properties.  Zinc,  and 


CONTENTS.  ix 

its  Combinations.  Acidifiable  Metals.  Arsenic,  Chrome  and  An- 
timony; their  properties  and  uses.  Medicines  and  Figments  ob- 
tained from  Metals.  192 


CONVERSATION  XX. 

OUT  AFFINITY,  AND  THE  LAWS  WHICH  GOVERN  CHEMICAL  COMBINATIONS. 

Action  of  the  Voltaic  Battery  upon  Alkaline  Salts.  Acids  passed 
through  Alkaline  Solutions,  without  combination.  Nature  of  Che- 
mical Affinity.  Laws  by  which  it  is  governed.  Double  Elective 
Attraction.  Law  of  Definite  Proportions.  Atomic  Theory.  Com- 
bination of  Gases  by  Volumes.  Newton's  Opinion  respecting  ulti- 
mate Particles  or  Atoms.  Relative  weight  of  Atoms.  Comparison 
of  the  absolute  and  relative  weights.  Practical  advantages  of  the 
Law  of  Definite  Proportions.  204 

CONVERSATION  XXI. 

ON  THE  COMBINATIONS  OF  OXYGEN  AND  NITROGEN. 

Five  Combinations  of  Oxygen  and  Nitrogen.  State  of  the  two  Gases  in 
the  Atmosphere.  Oxygen  supplied  by  Growing  Vegetables.  Ato- 
mic Constitution  of  the  Compounds  of  Oxygen  and  Nitrogen.  Nitric 
Acid  formed  by  Nature.  Its  production  by  the  Electric  Spark. 
Mode  of  obtaining  it  from  Nitre.  Charcoal  and  Spirits  of  Turpen- 
tine fired  by  it.  Decomposition  of  Nitric  Acid  by  Heat  and  Light. 
Uses  of  Nitric  Acid.  215 


CONVERSATION  XXII. 

ON  THE  COMBINATIONS  OF  OXYGEN  AND  NITROGEN  (CONTINUED),  AND  ON 
NITKATES. 

Synthetical  and  Analytical  Examination  of  Bodies.  Nitrate  of  Copper. 
Nitric  Oxide,  Deutoxide  of  Nitrogen,  or  Nitrous  Air.  Nitrous  Acid. 
Eudiometrical  Property  of  Nitrous  Air.  Combustion  in  it.  Ab- 
sorbed by  Nitric  Acid.  Aquafortis.  Hyponitrous  Acid.  Nitrous 
Oxide.  Formation  and  decomposition  of  Nitrate  of  Ammonia.  Com- 
bustion in  Nitrous  Oxide.  Its  effects  when  inhaled.  Table  of  the 
Compounds  of  Oxygen  and  Nitrogen.  Nitrate  of  Potassa,  Nitre,  or 
Saltpetre.  Nitrate  of  Lime.  Nitre  Caves,  Incombustibility  of  Nitre. 
Oxygen  Gas  obtained  from  it.  Deflagration.  Gunpowder.  Deto- 
nation. Fulminating  Powder.  Uses  of  Nitre.  Properties  of  the 
Nitrates.  Combustion  of  Tin  Foil  by  Nitrate  of  Copper.  221 


CONVERSATION  XXIH. 

ON    OTANOGEN,    SELENIUM,    BORON,    FLUORIC    ACID,    MURIATIC     ACID,     AND 
CHLORINE. 

Cyanogen,  or  Bicarburet  of  Nitrogen.  Hydrocyanic,  or  Prussie  Acid. 
Hydrogen,  an  acidifying  principle.  Hydracids.  Prussian  Blue. 
Prussie  Acid  in  Vegetables.  Cyanic  Acid.  Selenium.  Boracic 


CONTENTS. 

Acid.  Borate  of  Soda,  or  Borax.  Boron.  Fluoric  Acid.  Fluate 
of  Lime,  or  Derbyshire  Spar.  Silex  and  Glass  dissolved  by  Fluoric 
Acid.  Etching  upon  Glass.  Fluo-silicic  Acid  Gas.  Fluorine,  the 
unknown  Base  of  Fluoric  Acid.  Muriatic  Acid,  or  Spirit  of  Sea 
Salt.  First  procured  in  its  Gaseous  Form  by  Priestley.  Obtained 
from  Muriate  of  Soda.  Description  of  Woulfe's  Apparatus.  Oxy- 
muriatic  Acid,  or  Chlorine.  Combustion  of  Metals,  and  of  Phos- 
phorus in  this  Gas.  Its  Bleaching  Properties.  Theory  of  its  pro- 
duction. Two  Theories  respecting  its  Nature.  Proofs  that  it  does 
not  contain  Oxygen.  Effect  of  Light  upon  a  Mixture  of  Gaseous 
Chlorine  and  Hydrogen.  Common  mode  of  obtaining  Chlorine. 


CONVERSATION  XXIV. 

ON  THE  COMPOUNDS  OF  CHLORINE,    AND    ON    IODINE,    BROMINE,    AND    THEIR 
COMPOUNDS. 

Chlorides  and  Muriates.  Hydrochloric  Acid.  Chlorine  and  Oxygen. 
Protoxide  of  Chlorine.  Chloric  and  Perchloric  Acids.  Chloride 
of  Nitrogen.  Hydrocarburet  of  Chlorine.  Chlorate,  or  Hyperoxy- 
muriate  of  Potassa.  Affords  pure  Oxygen.  Match-lights.  Com- 
bustion of  Phosphorus  under  Water.  Detonations  with  Sulphur, 
Phosphorus,  and  Metals.  Percussion  Powder.  Muriate  of  Soda, 
or  Chloride  of  Sodium.  Sea  Water.  Sources  and  Uses  of  Common 
Salt.  Muriate  of  Ammonia.  Muriate  of  Lime.  Chloride  of  Lime. 
Its  Bleaching  and  Disinfecting  Properties.  Aqua  Regia,  or  Nitro- 
xnuriatic  Acid.  Dissolution  of  Gold.  Corrosive  Sublimate,  and 
Calomel.  Iodine  and  Bromine.  Their  Properties  and  Combina- 
tions. Are  Electro-negative  Bodies.  Uses  of  Iodine.  241- 


CONVERSATION   XXV. 

ON  THE   GENERAL  PROPERTIES  OF  SALTS. 

Of  what  a  Salt  must  consist.  What  were  formerly  called  Salts.  Sa- 
pidity of  Salts  dependent  upon  their  Solubility.  Circumstances 
which  control  the  Solubility  of  a  Salt.  Deliquescence,  Efflorescence, 
and  Permanence.  Water  of  Crystallization.  Anhydrous  Salts.  Ef- 
fect of  hot  Water  in  dissolving  Salts.  Formation  of  Regular  Crys- 
tals. Two  Solid  Salts  rendered  fluid  by  Mixture.  Incompatible 
Salts.  Separation  of  Salts  from  each  other.  Salts  dissolved  in  a 
saturated  Solution.  Double  Salts.  Definition  of  a  Crystal.  Some 
Crystals  not  imitable  by  art. 

CONVERSATION  XXVI. 

ON  CRYSTALLOGRAPHY. 

Advantages  derived  from  Crystallography.  Bodies  in  general  suscep- 
tible of  Crystallization.  Different  Forms  assumed  by  different 
Bodies.  Primary  and  Secondary  Forms.  Integrant  Particles,  or 
Molecules.  Derivation  of  the  Rhombic  Dodecahedron  from  the 
Cube.  Conversion  of  the  Octahedron  into  a  Cube,  and  of  the  Cube 
into  an  Octahedron  by  mechanical  Division.  Dr  Wollaston's  Theory 
of  the  Formation  of  Crystals  from  Spherical  Particles.  Exemplified 


CONTENTS.  xi 

in  the  Piling  of  Balls.     Illustration  of  the  Production  of  variour 
Crystalline  Forms  in  this  way.  259 

CONVERSATION  XXVII. 

ON  THE  STEAM  ENGINE. 

Steam  used  to  produce  Motion  by  Hero  of  Greece.  Mr  Watt,  the 
greatest  improver  of  the  Steam  Engine.  Admission  of  Steam  alter- 
nately above  and  below  a  Piston  in  a  Cylinder.  The  Steam  Pipe, 
Eduction  Pipe,  Condenser,  and  Air  Pump.  Low  Pressure  Engine. 
Mode  of  setting  an  Engine  to  work.  Rotary  produced  by  a  Vibra- 
tory Motion.  Safety  Valve.  Atmospheric  Engine.  Watt's  En- 
gine. Fly  Wheel.  Parallel  Motion.  Nature  of  the  High  Pressure 
Engine.  '  266 


CONVERSATION  XXVIII. 

ON  ORGANIZED  BODIES,  AND  VEGETABLE  CHEMISTRY. 

Organs  of  Animals  and  Vegetables.  Composition  of  Organic  Sub- 
stances. Chemical  Affinity  controlled  by  Vitality.  Destructive 
Distillation,  and  Spontaneous  Decomposition.  Proximate  and  Re- 
mote Principles.  Vegetable  Principles  divided  into  three  classes. 
List  of  some  of  them.  Vegetable  Acids, — Oxalic,  Tartaric,  Citric, 
Benzoic,  Gallic,  &c.  Formation  of  Ink.  Vegetable  Alkalies;  Mor- 
phia and  Narcotine;  Quinia  and  Cinchonia.  Oils,  Fixed,  Drying, 
Volatile  or  Essential.  Camphor.  Resins.  Varnishes.  Amber. 
Caoutchouc  or  Gum-elastic.  Wax.  Bitumens.  Naphtha.  Pe- 
troleum. Mineral  Tar.  Pitcoal.  Anthracite.  Coke.  278 


CONVERSATION  XXIX. 

ON  VEGETABLE  CHEMISTRY — CONTINUED. 

Vegetable  Principles  of  the  Third  Class.  Sugar  and  its  Manufacture. 
Molasses,  Loaf-sugar,  Sugar-candy,  and  Barley  Sugar.  Honey,  Su- 
gar of  Grapes,  and  Manna.  Gum  or  Mucilage.  Distinction  be- 
tween Gums  and  Resins.  Fecula  or  Starch,  Arrow  Root,  Tapioca, 
and  Sago.  Fecula  converted  into  Sugar  by  Sulphuric  Acid,  by 
Fermentation,  and  by  Germination!  Malting.  Gluten.  Tannin. 
Lignin  or  Woody  Fibre.  Colouring  Matter,  Lakes,  and  Dyeing. 
Adjective  and  Substantive  Colours  and  Mordants.  Fermentation. 
Saccharine.  Vinous.  Use  of  Yeast.  Nature  and  Combustion  of 
Alcohol.  Ethers.  Sulphuric  Ether.  A  phlogistic  Lamp.  Acetous 
Fermentation,  Acetic  Acid,  Vinegar,  and  Pyroligneous  Acid.  Pro- 
ducts of  the  Putrefactive  Fermentation.  290 


CONVERSATION  XXX. 

ON   ANIMAL  CHEMISTRY. 

The  Constituent  Principles  of  Animal  Matter  found  in  Vegetables. 
Their  Proximate   Principles  more  complex.    Fibrin.    Albumen. 


xii  CONTENTS. 

Fining  of  Wine,  Coffee,  &c.  Gelatin,  Glue,  and  Ichthyocolla.  Os* 
mazome.  Process  of  Tanning.  Acids  existing  in  the  Animal  Sys- 
tem. Animal  Oils  and  Fats.  Stearine  and  Elaine.  Margaric  and 
Oleic  Acids.  Glycerine.  Adipocere.  Formation  of  Oils  from 
their  Constituents.  Milk,  Cream,  Caseous  Matter  or  Curd,  Whey, 
and  Rennet  299 


CONVERSATION  XXXI. 

ON  DIGESTION,    SECRETION,    ANIMAL  HEAT,  &C. 

Formation  of  Chyme  and  Chyle.  Bile,  its  secretion  and  use.  The 
Gastric  Juice.  Its  remarkable  solvent  power.  Circulation  of  the 
Blood.  Arterial  and  Venous  Blood.  Change  produced  in  the 
Blood  by  Respiration.  Priestley's  Experiments  on  the  Effects  of 
Oxygen  on  Venous  Blood.  Permeability  of  Membranes.  Carbonic 
Acid  exhaled  from  the  Lungs.  Animal  Heat  influenced  by  Respira- 
tion. Conclusion.  306 

Glossary  of  Chemical  Terms. 


on 


CONVERSATION  I. 

ON  THE  GENERAL  PRINCIPLES  OF   CHEMISTRY. 

V>*C//-  7 
Intimate  connexion  of  Chemistry  and  Mechanical  Philosophy.      Chemistry 

as  a  Science  and  as  an  Art.  Ancient  and  Modern  Chemistry.  Difference 
between  Mechanical  and  Chemical  Action.  Definition  of  Chemistry.  Simple 
and  Compound  Sadies.  Analysis  and  Synthesis.  Chemical  Attraction. 
Affinity,  or  Elective  Attraction. 

Mrs  B.  As  you  have  already  acquired  some  knowledge  of  the  elemen- 
tary principles  of  Natural  Philosophy,  I  now  propose  to  direct  your  attention 
to  a  kindred  branch  of  science,  the  study  of  which  will  equally  reward  you 
for  your  exertions  —  I  mean  Chemistry.  You  will  find  this  science  to  be  so 
intimately  connected  with  Natural  Philosophy,  as  to  open  to  you  new  views 
upon  that  subject,  and  to  convince  you  that  an  acquaintance  with  the  one  must 
he  very  incomplete  without  a  corresponding  familiarity  with  the  other(l). 
Natural  Bhilosophy  explains  the  general  laws  by  which  bodies  are  gov- 
erned, in  their  sensible  motions;  but  the  ideas"which  you  form  of  the  bodies 
themselves  must  be  very  defective,  if  you  remain  totally  ignorant  of  the 
nature  of  the  substances  of  which  they  are  composed. 

Caroline.  Although  the  study  of  chemistry  has  become  very  fashionable, 
and  I  have  no  doubt  is  sufficiently  amusing,  yet  to~  confess  the  truth,  Mrs  B. 
after  seeing  nature  exhibited  on  a  magnificent  scale  in  the  revolutions  of 
those  immense  masses,  the  planetary  orbs;  after  examining  the  laws  by 
which  they  operate  upon  each  other,  notwithstanding  the  millions  of  miles 
by  which  they  are  separated,  I  cannot  help  turning  to  the  petty  details  of 
the  distiller,  the  compounder  of  medicines,  and  the  manufacturer  of  per- 
fumes, with  a  feeling  of  their  comparative  littleness,  and  a  conviction  that 
they  are  not  calculated  to  excite  in  the  mind  those  sentiments  of  grandeur 
and  sublimity,  which  result  from  the  contemplation  of  the  mechanism  of  the 
universe. 

Mrs  B.  You  appear  to  me,  my  dear  Caroline,  to  be  somewhat  too  imagi- 
native in  your  views,  and  I  think  you  will  by  and  bye  confess  that  the  little 
value  which  you  are  at  present  disposed  to  place  upon  chemistry  results  en- 
tirely from  the  limited  idea  which  you  entertain  of  its  object.  You  also 
seem  to  confound  together  two  things  which  differ  essentially,  chemistry 
as  a  science,  and  chemistry  as  an  art(2).  The  latter  is  frequently  pursued 
by  persons  unacquainted  with  its  principles;  whilst  as  a  science,  it  has 
commanded  the  attention,  and  rewarded  the  inquiries  of  men  of  the  most 


1.  With  what  other  department  of  science  is  chemistry  most  intimately 
connected,  and  what  advantage  will  result  from  an  acquaintance  with  it? 

2.  Chemistry  may  be  divided  into  two  departments,  what  are  the*  ? 

B 


14  CONVERSATIONS  ON  CHEMISTRY. 

exalted  talents(3).  Nature  has  the  universe  for  her  laboratory,  in  which  she 
is  continually  employed  in  chemical  operations,  producing  effects  as  inte- 
resting, as  wonderful,  and  equally  necessary  with  those  which  belong  to 
Natural  Philosophy(4). 

The  study  of  the  works  of  nature  is  divided  into  three  grand  branches — 
Natural  History,  Natural  or  Mechanical  Philosophy,  and  Chemistry(5). 
The  first  teaches  us  to  distinguish  bodies  from  each  other  by  their  external 
forms  and  charaeters(G);  the  second  inquires  into  the  effects  produced  by 
bodies  upon  each  other,  from  their  mechanical  action  only,  such  as  their 
gravity,  weight,  and  motion(7); — the  third,  Chemistry,  examines  into  the  in- 
timate nature  of  bodies,  that  is,  into  the  nature  of  the  materials  of  which  all 
bodies  are  composed(S);  and  I  have  no  doubt  you  will  soon  agree  with  me  in 
thinking  it  the  most  interesting  of  the  three.  You  may  easily  conceive, 
therefore,  that  without  entering  into  the  minute  details  of  practical  chemis- 
try, you  may  obtain  such  a  knowledge  of  this  science  as  will  not  only  excite 
a  new  interest  in  the  common  occurrences  of  life,  but  will  also  enlarge  the 
sphere  of  your  ideas,  and  render  the  contemplation  of  nature  a  source  of 
delightful  instruction. 

Caroline.  I  confess  that  I  am  already  convicted  of  having  been  too  pre- 
cipitate in  the  judgment,  or  rather  in  the  notion,  which  I  had  formed  of 
chemistry;  for  although  I  knew  that  it  was  not  entirely  confined  to  the  art 
of  preparing  drugs  and  other  compounds,  yet  I  considered  this  as  its  prin- 
cipal object. 

Mrs  B.  There  is  a  branch  of  practical  chemistry  called  Pharmacy, 
which  relates  exclusively  to  the  preparing  of  medicine,  and  it  is  undoubtedly 
an  art  of  great  importance  to  professional  men,  and  indeed  to  the  world  at 
large(9);  but  in  studying  chemistry  as  a  science,  we  have  no  more  to  do  with 
this  as  an  art,  than  we  have  with  the  method  of  grinding  glasses,  when  ac- 
quiring a  knowledge  of  optics. 

Emily.  I  have  frequently  read  of  the  alchemists,  and  their  endeavours  to 
discover  the  philosopher's  stone,  and  the  art  of  making  gold;  pray  what  is 
the  difference  between  these  men  and  the  modern  chemists? 

Mrs  B.  The  alchemists  were  a  set  of  misguided  philosophers,  who  as- 
sumed this  name  to  distinguish  themselves  and  their  pursuits  from  the 
common  chemists,  whose  studies  were  then  confined  to  the  knowledge  of 
medicines(lO). 

Many  of  the  alchemists  were  men  of  great  genius,  but  their  pursuits  par- 
took largely  of  the  ignorance  of  the  dark  ages  in  which  they  lived,  being 
generally  intermingled  with  the  exploded  notions  of  magic,  and  astrology. 
Their  whole  proceedings  were  consequently  involved  in  mystery  and  secrecy  ^ 
but  since  that  period  chemistry  has  undergone  so  complete  a  revolution, 
that  from  an  obscure  and  mysterious  art,  it  has  now  become  a  regular  and 
beautiful  science,  comprehending  in  the  sphere  of  its  inquiries  the  nature 
of  every  substance  found  in  the  material  world(ll). 

The  alchemists  imagined  that  all  metals  contained  one  common  principle, 
and  that  the  difference  between  them  arose  from  the  combination  of  this  prin- 
ciple with,  certain  impurities:  it  was  only  necessary,  therefore,  to  remove 
these,  in  order  to  the  conversion  of  either  Q£  them  into  gold,  the  making 


3.  What  is  remarked  of  the  persons  who  pursue  them  respectively? 

4.  What  is  said  of  the  laboratory  of  nature? 

5.  What  are  the  three  grand  divisions  of  the  study  of  the  works  of  nature? 

6.  What  does  the  first  teach? 

7.  What  the  second?     8.  What  the  third?     9.  What  is  Pharmacy? 

10.  What  were  the  alchemists,  and  what  their  pursuits? 

11.  What  change  has  chemistry  undergone  since  their  'fcy? 


GENERAL  PRINCIPLES.  15 

of  which  precious  metal  was  the  great  object  of  their  researches.  The 
philosopher's  stone,  which  they  hoped  to  form  or  to  discover,  was  to  he  the 
substance  with  which  they  were  to  accomplish  this  grand  design(12). 

Although  these  visionary  schemes  entirely  failed,  yet  the  labours  of  the 
alchemist  were  not  performed  in  vain.  Scarcely  any  known,  substance 
escaped  their  investigations,  and  years  were  sometimes  devoted  to  a  single 
experiment.  The  result  of  this  industry  was,  the  discovery  of  the  greater 
number  of  the  active  preparations  used  by  the  physician,  and  numerous 
valuable  compounds  employed  in  the  arts.  They  were  thus  the  means  of 
increasing,  to  a  wonderful  extent,  the  conveniences  and  luxuries  of  life(13). 

Caroline.  Do  pray,  madam,  tell  us  more  precisely  in  what  manner  the 
discoveries  of  the  alchemists,  and  of  the  chemists,  have  proved  so  beneficial 
to  society. 

J\frs  B.  Patience,  my  child;  you  would  not  now  be  able  to  comprehend 
the  nature  of  their  discoveries,  although  they  may  hereafter  be  rendered 
quite  easy  and  familiar  to  you.  In  order  to  this,  however,  we  must  pay  a 
due  regard  to  method,  as  without  it  you  will  not  be  able  to  make  any  pro- 
gress in  chemistry.  I  shall,  in  the  first  place,  explain  to  you  some  of  the 
chemical  operations  of  nature;  from  these,  the  transition  to  those  of  art  will 
become  quite  easy,  and  they,  also,  are  sufficiently  important  to  claim  a  large 
share  of  our  attention. 

Emily.  Well,  then,  let  us  now  set  to  work  regularly?  I  am  very  anxious 
to  begin,  and  shall  be  obliged  by  your  first  giving  us  a  more  distinct  idea  of 
the  difference  between  natural  philosophy  and  chemistry. 

•Mrs  B.  Natural  philosophy,  in  its  most  comprehensive  sense,  would 
embrace  both  these  departments  of  science,  and  they  were  in  fact  both  in- 
cluded under  this  term,  until  the  progress  of  chemistry  gave  to  it  a  just 
claim  to  rank  as  a  distinct  department(l4).  The  name  mechanical  philoso- 
phy is  now  generally  substituted  for  natural  philosophy,  and  ought  to  be  so, 
uniformly;  as  all  the  changes  that  take  place  in  bodies  which  are  not  che- 
mical are  mechanical,  whilst  they  are  both  perfectly  natural(15). 

We  perpetually  see  many  of  the  substances  in  nature  changing  their  pro- 
perties, appearing  to  be  transmuted,  or  converted  into  others  which  bear 
little  or  no  resemblance,  either  inform  or  substance,  to  the  materials  from 
which  they  were  produced(16).  Thus  iron,  when  exposed  to  air  and  mois- 
ture, becomes  converted  into  a  brown  earthy  substance,  which  we  call  rust(17); 
our  candles  also,  and  other  combustibles,  when  burned,  appear  to  be  anni- 
hilated, or  put  out  of  existence(lS),  an  event,  the  impossibility  of  which  you 
have  already  learned  in  your  natural  philosophy. 

Chemistry  investigates  the  nature  and  causes  of  those  changes  •which 
take  place  in  the  intimate  nature,  or  composition  of  bodies,  -whether  these 
changes  be  slowly  or  rapidly,  naturally  or  artificially produced(19). 

A  substance  may  be  broken  into  pieces,  it  may  be  reduced  into  the  finest 
powder,  or  it  may  be  removed  from  one  place  to  another,  by  mechanical 
force,  without  any  other  change  in  it  than  that  of  size,  or  place;  but  when- 
ever a  body  is  so  acted  upon  as  to  have  its  nature  altered,  the  action  is  cAe- 


12.  What  idea  did  they  entertain  respecting  the  metals? 

13.  What  advantage  has  the  world  derived  from  their  pursuits? 

14.  What  might  be  comprehended  in  the  term  natural  philosophy? 

15.  What  is  natural  philosophy  now  called,  and  what  renders  it  proper? 

16.  What  changes  do  we  perpetually  witness? 

17.  What  is  the  first  example  given? 

18.  What  the  second? 

19  What  are  the  objects  of  chemical  investigation? 


16  CONVERSATIONS  ON  CHEMISTRY. 

tra'caZ(20).  You  will  find,  therefore,  Caroline,  that  chemistry  is  no  narrow- 
er confined  science,  but  that  it  comprehends  every  thing  material  within 
our  sphere  of  observation. 

Caroline.  It  must  indeed  be  inexhaustible,  and  I  am  now  at  a  loss  to 
conceive  how  any  proficiency  can  be  made  in  a  science  whose  objects  are 
BO  numerous. 

Mrs  B.  If  every  individual  substance  were  formed  of  different  materials, 
the  study  of  chemistry  would,  indeed,  be  endless;  but  you  must  observe 
that  the  various  bodies  in  nature  are  composed  of  certain  simple  substances, 
or  elementary  principles,  which  are  not  very  numerous(21). 

Caroline.  Yes;  I  know  that  all  bodies  are  composed  of  fire,  air,  earth 
and  water;  I  learnt  that  many  years  ago(22). 

Mrs  B.  But  you  must  now  endeavour  to  forget  it.  I  have  already  in- 
formed you  how  great  a  change  chemistry  has  undergone  since  it  has 
become  a  regular  science.  Within  these  forty  years  especially,  it  has  ex- 
perienced an  entire  revolution,  and  it  is  now  proved  that  neither  fire,  air, 
earth,  or  water,  can  be  called  elementary  bodies.  An  elementary  body  is 
one  that  has  never  been  decomposed,  that  is  to  say,  separated  into  other 
substances(23).  Air,  earth,  and  water,  are  all  of  them  susceptible  of  decom- 
position, and  the  same  may  probably  be  asserted  of  fire(24). 

Emily.  I  thought  that  decomposing  a  body  was  dividing  it  into  its  mi- 
nutest parts.  And  if  so,  I  do  not  understand  why  an  elementary  substance 
is  not  capable  of  being  decomposed,  as  well  as  any  other. 

Mrs  B.  You  have  misconceived  the  idea  of  decomposition;  it  is  very 
different  from  mere  division.  The  latter  simply  reduces  a  body  into  parts, 
but  the  former  separates  it  into  the  various  ingredients,  or  materials,  of 
which  it  is  composed(25).  If  we  were  to  take  a  loaf  of  bread,  and  separate 
the  several  ingredients  of  which  it  is  made,  the  flour,  the  yeast,  the  salt, 
and  the  water,  it  would  be  very  different  from  cutting  or  crumbling  the 
loaf  into  pieces(26). 

Emily.  I  understand  you  now  very  well.  To  decompose  a  body  is  to 
separate  from  each  other  the  various  simple  or  elementary  substances  of 
•which  it  consists. 

Caroline.  But  flour,  water,  and  the  other  materials  of  bread,  according 
to  your  definition,  are  not  elementary  substances. 

Mrs  B.  No,  my  dear;  this  separation  of  the  ingredients  of  bread  would 
be  only  a  partial  decomposition;  but  it  may  serve  to  give  you  a  familiar 
idea  of  what  is  intended. 

The  elementary  substances  of  which  a  body  is  composed  are  called  the 
constituent  parts  of  that  body;  in  decomposing  it,  therefore,  we  separate  its 
constituent  parts(27).  If,  on  the  contrary,  we  divide  a  body  by  chopping  it 
to  pieces,  or  even  by  grinding  or  reducing  it  to  the  finest  powder,  each  of 
these  small  particles  will  still  consist  of  a  portion  of  the  several  constituent 
parts  of  the  whole  body:  these  are  called  the  integrant  parts(28);  do  you  un- 
derstand the  difference? 


20.  How  would  you  discover  whether  a  body  had  been  acted  upon  me- 
chanically or  chemically? 

21.  Are  all  substances  which  differ  formed  of  different  materials? 

22.  Of  what  elements  does  Caroline  suppose  all  bodies  to  be  formed? 

23.  What  is  meant  by  an  elementary  substance? 

24.  What  is  said  respecting  what  were  once  called  the  four  elements? 

25.  What  is  the  difference  between  mere  division  and  decomposition' 

26.  Give  the  example. 

27.  What  is  meant  by  the  constituent  parts  of  a  body? 

28.  What  by  integrant  parts? 


GENERAL  PRINCIPLES.  17 

Emily.  Yes.  I  think  perfectly.  We  decompose  a  body  into  its  consti- 
tuent parts,  and  divide  it  into  its  integrant  parts. 

Mrs  B.  Exactly  so.  If  therefore  a  body  consists  of  only  one  kind  of 
substance,  though  it  may  be  divided  into  its  integrant  parts,  it  is  not  possible 
to  decompose  it.  Such  bodies  are  therefore  called  simple  or  elementary, 
as  they  are  the  elements  of  which  all  other  bodies  are  composed.  Com- 
pound bodies  are  such  as  consist  of  more  than  one  of  these  elementary 
principles(29). 

Caroline.  Pray  what  is  the  difference  between  decomposing  and  analy- 
sing a  body?  so  far  as  I  understand  the  terms,  they  appear  to  be  perfectly 
synonymous. 

Mrs  .B.  But  they  are  not  so,  my  dear;  for  although  you  cannot  analyze 
a  compound  body  without  decomposing  it,  you  may  decompose  without  ana- 
lyzing it.  The  wood  and  coal  which  we  burn  in  our  fires  are  compound 
bodies,  and  are  decomposed  in  their  combustion;  but  they  are  not  analyzed. 
When  we  analyze  a  body,  we  do  not  allow  any  part  of  it  to  escape,  but 
collect  all  the  different  substances  into  which  it  can  be  resolved  by  decom- 
position, whether  they  be  solids,  liquids,  or  airs(SO). 

The  object  of  analysis  is  to  ascertain  of  -what  simple,  or  elementary  sub- 
stances a  body  is  composed,  and  the  relative  quantity  of  each,  -which  enters 
into  its  composition(3l). 

There  is  necessarily  one  class  of  bodies  which  we  cannot  decompose; 
they  are  what  we  have  denominated  simple;  and  when  any  substance  resists 
every  attempt  to  decompose  it,  we  then  place  it  in  this  class  of  bodies(32). 

Emily.  But  I  should  think  that,  after  all,  the  chemist  may  be  mistaken, 
and  give  us  a  list  of  simple  substances,  which  those  who  come  after  him 
may  find  to  be  compound. 

Mrs  B.  I  am  pleased  with  your  remark,  as  it  leads  me  to  tell  you  that 
it  is  not  pretended  that  all  the  bodies  which  are  classed  as  simple  are  abso- 
lutely so.  Some  which  were  formerly  so  classed,  are  now  known  to  be 
compounds;  it  is  probable,  therefore,  that  as  the  methods  and  instruments 
of  examination  are  improved,  the  class  of  simple  substances  may  be  either 
reduced  or  increased  in  number(33).  . 

Caroline.  I  remember  seeing  in  a  work  upon  chemistry,  which  I  took 
up  some  time  ago,  that  there  were  three  modes  by  which  a  judgment  was 
formed  respecting  the  compound  nature  of  a  substance;  one  of  them,  analysis, 
I  think  I  perfectly  understand,  and  should  like  to  know  something  about  the 
other  two;  these  I  think  were  synthesis  and  analogy(3b). 
1  Mrs  B.  Synthesis  is  the  very  reverse  of  analysis,  and  means  the  re-form- 
ing of  a  compound  body,  by  causing  the  simples  of -which  it  -was  compounded 
to  unite  together,  and  to  reproduce  the  same  substance,  identical  in  all  it* 
properties(35}.  When  we  can  both  decompose  and  recompose  a  body,  or  in 
other  words,  give  an  analytical  and  synthetical  proof  of  its  composition,  the 
evidence  is  viewed  as  complete(36). 

Caroline.     Although  I  do  not  pretend  yet  to  know  any  thing  of  chemistry, 


29.  What  are  those  bodies  which  cannot  be  decomposed,  and  what  are 
compounds? 

30.  State  the  difference  between  mere  decomposition  and  analysis. 

31.  How  is  analysis  defined? 

32.  What  circumstance  induces  us  to  term  bodies  simple? 

33.  Does  our  placing  a  body  in  this  class  necessarily  imply  that  it  is  so? 

34.  There  are  said  to  be  three  modes  of  judging  of  the  compound  nature 
of  a  body;  what  are  they  ? 

35.  What  is  synthesis? 

36.  When  do  we  view  the  evidence  of  the  composition  of  a  body  complete  ? 
B2  ? 


IS  CONVERSATIONS  ON  CHEMISTRY. 

I  think  that  I  can  perceive  the  use  which  the  chemist  makes  of  analogy,  as 
the  word  means  resemblance  or  similarity.  I  suppose  that  when  a  substance 
•which  has  not  yet  been  decomposed,  possesses  a  striking  resemblance  in 
some  of  its  distinguishing  properties  to  others  which  have  been  decomposed, 
it  is  then  classed  among  compound  bodies(37). 

Mrs  B.  Your  remark,  Caroline,  is  both  acute,  and  generally  speaking, 
correct;  the  chemist,  however,  would  not  class  anundecompoundedbody  with 
those  which  had  actually  been  decomposed.  You  must  therefore  consi- 
der the  list  of  simples  to  be  no  other  than  a  catalogue  of  undecompounded 
substances,  the  greater  number  of  which  are  most  probably  elementar)(38). 

Emily.  I  should  like  first  to  learn  the  names  of  all  the  substances  ac- 
counted simple,  so  that  I  may  understand  something  about  them  when  I 
meet  with  them  again,  as  we  proceed  with  the  study  of  chemistry;  I  hope, 
however,  that  they  are  not  very  numerous. 

Mrs  B.  I  think  that  it  would  fce  unwise  for  you  to  commence  by  learn- 
ing these  names,  as  there  are  about  fifty  of  them(39).  A  moment's  reflection 
must  convince  you  that  in  order  to  know  them  when  you  meet  with  them, 
you  must  first  become  in  some  measure  acquainted  with  them.  I  shall, 
therefore,  introduce  them  to  you,  either  individually  or  in  classes,  as  we 
examine  their  properties;  you  will  thus  the  more  readily  become  familiar 
with  them. 

Emily.  I  own  my  folly,  and  will  in  future  endeavour  to  think  more  cor- 
rectly before  1  tell  my  thoughts.  I  should  be  sadly  at  a  loss  to  pick  out 
fifty  strangers  by  merely  having  a  list  of  their  names.  But  are  the  whole 
of  these  fifty  substances  new  to  us? 

Mrs  B.  No  my  dear;  about  two-thirds  of  the  whole  number  belong  to  one 
class,  the  metals(40),  with  several  of  which  you  are  already  familiar;  others 
of  them  are  not  of  very  great  importance.  As  I  shall  endeavour  to  guide 
you  systematically,  J  think  you  will  find  that  all  the  difficulty  which 
you  apprehend  respecting  the  names,  not  of  these  simples  only,  but  of  the 
numerous  compounds  which  they  form,  will  entirely  vanish. 

Caroline.  As  in  natural  philosophy,  the  attractions  of  cohesion  and  of 
gravitation  act  a  most  important  part,  I  suppose  that  chemical  attraction,  or 
affinity,  which  you  formerly  named  to  us,  is  equally  influential  in  chemical 
operations(4l). 

Mrs  B.  You  are  perfectly  correct  Caroline,  and  although  you  are  at 
present  unacquainted  with  the  nature  of  most  of  the  simple  substances,  it 
will  be  necessary  to  anticipate  our  subject  in  some  degree,  and  speak  of 
them  as  though  you  knew  them. 

Chemical  attraction,  or  the  attraction  of  composition,  consists  in  the 
peculiar  tendency  which  bodies  of  a  different  nature  have  to  unite  with 
each  other.  It  is  by  this  force  that  all  the  compositions  and  decomposi- 
tions are  effected(42). 

The  attraction  of  cohesion  exists  only  between  particles  of  the  same  na- 
ture, whether  simple  or  compound;  thus  it  unites  the  particles  of  a  piece 
of  metal,  which  is  a  simple  substance,  and  likewise  the  particles  of  a  loaf 
of  bread,  which  is  a  compound.  The  attraction  of  composition,  on  the  con- 
trary, unites  and  maintains  in  a  state  of  combination,  particles  of  a  dissimilar 
nature.  It  is  this  power  that  forms  each  of  the  compound  particles  of  which 


37.  State  the  nature  of  the  judgment  by  analogy. 

38.  How  are  we  to  consider  the  list  of  simples? 
S9.  How  many  simple  substances  are  known? 

40.  How  many  of  them  belong  to  the  class  of  metals? 

41.  What  species  of  attraction  belongs  to  chemistry? 

42.  In  what  does  chemical  attraction  consist? 


GENERAL  PRINCIPLES.  19 

bread  consists;  and  it  is  by  tbe  attraction  of  cobesion  that  all  tbese  particles 
are  connected  into  a  single  mass(43). 

Emily.  The  attraction  of  cobesion,  tben,  is  the  power  which  unites  tbe 
integrant  particles  of  a  body;  the  attraction  of  composition  that  which 
combines  the  constituent  particles.  Is  it  not  80(44)!* 

J\frs  B.  Precisely:  and  observe  that  the  attraction  of  cobesion  unites 
particles  of  a  similar  nature,  without  changing  their  original  properties.  The 
result  of  such  a  union,  therefore,  is  a  body  of  the  same  kind  as  the  par- 
ticles of  which  it  is  formed;  whilst  tbe  attraction  of  composition,  by  com- 
bining particles  of  a  dissimilar  nature,  produces  compound  bodies,  quite 
different  from  any  of  their  constituents.  If,  for  instance,  I  pour  on  the 
piece  of  copper  contained  in  this  glass,  some  of  this  liquid,  which  is  sul- 
phuric acid,  (oil  of  vitriol,)  mixed  with  some  nitric  acid,  (aqua  fortis,)  the 
copper  will  be  dissolved  in  the  acid,  and  this  will  take  place  in  consequence  of 
the  strong  chemical  attraction  which  exists  between  the  particles  of  these  two 
substances.  Observe  the  internal  commotion  of  the  liquid,  and  the  colour- 
ed fumes  which  are  escaping.  The  process  going  on  is  too  complex  for 
you  now  to  understand;  but  every  particle  of  the  copper  is  uniting  with  a 
particle  of  the  sulphuric  acid,  and  when  they  are  combined  together,  they 
•will  form  a  new  body,  totally  different  from  either  the  copper  or  the  acid(45). 
The  acid  has,  in  this  case,  to  overcome,  not  only  the  resistance  which  the 
strong  cohesion  of  the  particles  of  copper  opposes  to  their  combination  with 
it,  but  also  the  weight  of  the  copper,  which  makes  it  sink  to  the  bottom  of 
the  glass,  and  prevents  the  acid  from  having  such  free  access  to  it  as  it 
•would  if  the  metal  was  suspended  in  the  liquid(46). 

Emily  The  acid  seems,  however,  to  overcome  both  these  obstacles 
•without  difficulty,  and  appears  to  be  very  rapidly  dissolving  the  copper. 

Jlfrs  B.  By  this  means  it  reduces  the  copper  into  more  minute  parts 
than  could  possibly  be  done  by  any  mechanical  power.  But  as  the  acid  can 
act  only  on  the  surface  of  the  metal,  it  will  be  some  time  before  the  union 
of  these  two  bodies  will  be  completed. 

You  may,  however,  already  see  how  totally  different  this  compound  is 
from  either  of  its  ingredients.  It  is  neither  colourless,  like  the  acid,  nor 
hard,  heavy,  and  ruddy,  like  the  copper;  and  if  you  were  to  taste  it,  you 
would  no  longer  perceive  any  of  the  sourness  of  the  acid.  It  has  at  present 
the  appearance  of  a  blue  liquid;  but  when  the  union  is  completed,  and  the 
water  with  which  the  acid  is  diluted  is  evaporated,  the  compound  will  as- 
sume the  form  of  regular  crystals  of  a  fine  blue  colour,  and  perfectly  trans- 
parent^?). Of  these  I  can  show  you  a  specimen,  as  I  have  procured  some 
for  that  purpose.  These  crystals  are  sulphate  of  copper,  commonly  called 
blue  vitriol,  one  of  the  metallic  salts. 

Caroline.     How  beautiful  they  are  in  colour,  form,  and  transparency! 

Emily.  Nothing  can  be  more  striking  than  this  example  of  chemical  at- 
traction. ;», 

J\frs  B.  The  term  attraction  has  been  lately  introduced  into  chemistry 
as  a  substitute  for  the  word  affinity,  to  which  latter  name  some  chemists 
objected,  because  it  originated  in  the  vague  notion  that  chemical  combina- 
tion depended  upon  a  certain  resemblance  or  relationship  between  the  par- 
ticles of  the  different  bodies  that  are  disposed  to  unite;  an  idea  more  fanciful 


43.  How  are  the  attractions  of  cohesion  and  of  composition  distinguished? 

44.  What  do  they  respectively  unite? 

45.  What  experiment  may  we  perform  to  exhibit  the  nature  of  chemical 
attraction  ? 

46.  What  powers  has  the  acid  in  this  case  to  overcome?  f 

47.  What  are  the  striking  changes  produced? 


20  CONVERSATIONS  ON  CHEMISTRY. 


than  just.  Without  discussing  this  point  very  minutely,  let  it  be  agreed 
that  we  may  use  the  terms  affinity,  chemical  attraction,  and  attraction  of 
composition,  indifferently,  provided  we  recollect  that  they  have  all  the 
same  meaning  (48). 

Emily.  I  do  not  conceive  how  bodies  can  be  decomposed  by  chemical 
attraction.  That  this  power  should  be  the  means  of  composing  them  is 
very  obvious;  but  that  it  should,  at  the  same  time,  produce  exactly  the  con- 
trary effect,  appears  to  me  very  singular. 

Mrs  B.  To  decompose  a  body  is,  you  know,  to  separate  its  constituent 
parts,  which,  as  we  have  just  observed,  cannot  be  done  by  mechanical  means. 

Emily.  No:  because  mechanical  means  separate  only  the  integrant  par- 
ticles; they  act  merely  against  the  attraction  of  cohesion,  and  only  divide  a 
compound  into  smaller  parts. 

Mrs  If.  The  decomposition  of  a  body  is  performed  by  chemical  powers. 
If,  to  a  body  composed  of  two  principles,  JTOU  present  a  third,  which  has  a 
greater  affinity,  or  attraction,  for  one  of  them  than  the  two  first  have  for  each 
other,  it  will  be  decomposed,  that  is,  its  two  principles  will  be  separated 
by  means  of  the  third  body  (49).  Let  us,  to  illustrate  this  point,  take  a  por- 
tion of  common  soap,  which  consists  of  oily  matter  or  fat,  united  to  an  alkali. 
You  know  that  soft  soap  is  made  by  boiling  grease  and  ley  together;  this  ley 
contains  the  alkali  called  potash,  which,  uniting  with  the  grease,  forms  soap. 
If  I  drop  a  portion  of  any  strong  acid  into  some  soap  suds,  the  soap  will  be  de- 
composed, because  the  acid  has  a  stronger  affinity  for  the  alkali  than  the 
latter  has  for  the  grease. 

I  will  now  drop  some  nitric  acid  into  these  soap  suds:  you  see  the  grease 
immediately  separated,  and  appearing  like  oil  upon  the  surface  (50). 

Caroline.  That  is  a  very  satisfactory  experiment;  but  as  the  nitric  acid 
and  the  potash  have  united,  I  should  like  to  know  what  new  compound  is 
formed  by  their  combination. 

Mrs  B.  They  have  formed  a  kind  of  salt,  which  the  chemist  calls  nitrate 
of  potash,  and  which  you  know  as  nitre  or  saltpetre  (51). 

Emily.  Could  we  contrive,  by  any  means,  to  separate  the  saltpetre  from 
the  water  and  the  grease?  I  should  be  delighted  to  be  able  to  do  this. 

Mrs  B.  Were  we  to  drop  in  just  enough  acid  to  decompose  the  whole 
of  the  soap,  we  might  then  separate  the  grease,  and,  on  evaporating  the 
water,  we  should  obtain  crystals  of  common  nitre  (52). 

Caroline.  And  can  you  decompose  the  sulphate  of  copper,  and  as 
readily  and  plainly  restore  the  copper  to  its  natural  state,  as  you  did  the 
grease  in  the  last  experiment? 

Mrs  B.  Very  readily  indeed.  When  we  wish  to  decompose  the  com- 
pound we  have  just  formed  by  the  combination  of  the  two  ingredients, 
copper  and  sulphuric  acid,  we  may  do  it  by  putting  into  the  liquid  a  piece 
of  iron,  for  "which  metal  the  acid  has  a  stronger  attraction  than  for  copper; 
the  acid  will,  consequently,  quit  the  copper  to  combine  with  the  iron,  and  the 
copper  will  be,  what  the  chemists  call,  precipitated;  that  is  to  say,  it  will 
be  separated  and  descend  to  the  bottom  of  the  vessel  (53),  and  appear  in  itn 
simple  form. 

In  order  to  produce  this  effect,  I  shall  dip  the  blade  of  this  knife  into  the 
fluid,  and,  when  I  take  it  out,  you  will  observe  that  instead  of  being  wetted 


48.  What  three  terms  are  used  synonymously? 

49.  How  may  a  body  composed  of  two  principles  be  decomposed^ 

50.  Furnish  the  example  given. 

51.  What  new  combination  is  formed? 

52.  How  could  this  salt  be  separated? 

53.  What  is  meant  by  precipitation? 


GENERAL  PRINCIPLES.  21 

'ith  a  bluish  liquid,  like  that  contained  in  the  glass,  it  will  be  covered 
vith  a  thin  coat  of  copper  (54). 

Caroline.  So  it  is  really!  but  then  is  it  not  the  copper,  instead  of  the 
acid,  that  has  combined  with  the  iron? 

Mrs  B.  No;  you  are  deceived  by  appearances:  it  is  the  acid  which 
combines  with  the  iron,  and  in  so  doing,  deposites  or  precipitates  the  cop- 
per on  the  surface  of  the  blade;  and  were  we  to  allow  the  blade  to  remain 
in  the  fluid  for  some  time,  the  whole  of  the  copper  would  be  separated  from 
the  acid,  a  corresponding  portion  of  the  iron  being  dissolved,  and  forming 
by  its  union  with  the  acid  sulphate  of  iron,  or  common  copperas(55). 

Emily.  But  cannot  three  or  more  substances  combine  together,  without 
any  of  them  being  precipitated? 

Mrs  B.  This  very  frequently  occurs,  and  in  the  course  of  our  inquiries 
you  will  meet  with  several  examples.  There  are,  for  instance,  but  few 
rocks  or  stones  which  do  not  consist  of  more  than  two  ingredients  chemi- 
cally combined  together.  All  salts,  also,  and  indeed  the  greater  number  of 
chemical  compounds,  may  be  resolved  into  three  or  more  simples(56). 

Caroline.  But  pray,  Mrs  B.,  what  is  the  cause  of  the  chemical  attrac- 
tion of  bodies  for  each  other?  It  appears  to  me  more  extraordinary,  or 
unnatural,  if  I  may  use  the  expression,  than  the  attraction  of  cohesion, 
which  unites  particles  of  a  similar  nature. 

Mrs  B.  Chemical  attraction  may,  like  that  of  cohesion  or  gravitation, 
he  one  of  the  powers  inherent  in  matter,  which,  in  our  present  state  of 
knowledge,  admits  of  no  other  satisfactory  explanation  than  an  immediate 
reference  to  a  d"ivine  cause(57).  Some  plausible  and  ingenious  theories 
have  been  devised  upon  this,  as  well  as  upon  almost  every  other  subject; 
hut  until  you  are  acquainted  with  all  the  known  facts,  and  your  judgments 
have  become  matured  by  time  and  reflection,  such  speculations,  instead 
of  increasing  your  knowledge,  would  retard  your  progress.  Of  causes,  we 
may  aver  that  we  really  know  nothing.  We  say,  indeed,  that  gravitation 
causes  a  stone  to  descend;  but  if  we  inquire  what  causes  gravitation,  we 
find  that  upon  this  point  we  have  arrived  at  the  end  of  our  natural  philoso- 
phy, and  are  compelled  to  resolve  the  whole  into  the  will  of  the  Creator  (58). 

Emily.  The  subject  of  affinity  appears  to  me  to  be  very  curious  and  in- 
teresting, and  I  should  like  to  know  a  great  deal  more  about  it  before  we 
enter  upon  any  other.  Although  your  examples  seem  to  be  very  clear,  I 
can  yet  scarcely  comprehend  how  the  same  power  should  produce  combi- 
nation and  decomposition. 

Caroline.  Let  me  try  whether  I  cannot  explain  it  by  what  appears  to  me 
to  be  a  striking  simile.  I  hold  this  apple  in  my  hand,  but  some  one  strong- 
er than  I  am  might  take  it  from  me;  and  so  a  third  or  a  fourth  might  in 
succession  obtain  it,  and  each  by  the  same  kind  of  power,  but  different  in 
degree(59). 

Mrs  B.  Your  simile  is  a  very  happy  one,  and  I  am  pleased  to  find  you 
both  so  much  interested  in  the  subject  of  the  attraction  of  composition.  We 
might  devote  a  considerable  portion  of  time  to  the  laws  which  obtain  in  the 


54.  How  can  the  copper  of  the  sulphate  of  copper  be  separated? 

55.  What  becomes  of  the  iron? 

56.  Are  there  many  instances  in  which  more  than  two  simples  combine 
to  produce  a  new  substance? 

57.  Are  we  acquainted  with  the  cause  of  chemical  attraction? 

58.  Can  we,  properly  speaking,  be  said  to  know  the  cause  of  any  natural 
phenomenon  ? 

59.  By  what  simile  is  the  power  of  attraction  in  producing  decomposi- 
tion illustrated? 


22  CONVERSATIONS  ON  CHEMISTRY. 

chemical  combination  of  bodies;  but  as  every  process  which  I  shall  either 
perform  or  explain,  will  serve  to  exemplify  one  or  more  of  these  laws,  I 
shall  have  ample  and  better  opportunities  of  rendering  them  familiar,  than 
by  dwelling  upon  them  now.  Some  of  them  I  shall  reserve  until  you  have 
acquired  a  considerable  portion  of  knowledge  in  the  elements  of  chemistry. 
Before  passing  to  another  s«4bject,  I  will  explain  to  you  the  acceptation  in 
which  the  term  elective  is  used  by  chemists. 

Elective  affinity,  or  elective  attraction,  you  will  find  spoken  of  in  every 
work  upon  chemistry.  The  word  elective  is  employed  to  express  the 
choice  which  any  particular  substance  seems  to  make  in  uniting  to  one 
body  in  preference  to  another,  although  it  may  actually  possess  an  affinity 
to  each.  It  is,  therefore,  only  another  form  of  expressing  the  fact,  that  a 
body  possessing  an  attraction  towards  a  number  of  others,  possesses  it  in 
different  degrees(6Q). 

Emily.  I  am  afraid  that  I  shall  never  be  able  to  remember  what  bodies 
attract  each  other  with  the  greatest  force,  $nd  without  this  I  shall  never 
know  by  what  means  to  separate  any  two  substances  which  have  combined 
together. 

Mrs  B.     The  most  able  chemists  do  not  pretend  to  recollect  all  the  facts 
upon  this  subject;  but  they  have  constructed  tables  in  which  the  several 
substances  with  which  a  particular  body   will  combine,    are  placed  in  the 
order  of  their  attractions(Gl),   as  may  be  seen  in  this  example,   in  which  is 
shown  the  affinity  of  nitric  acid  for  several  of  the  metals. 
Nitric  Acid. 
Iron, 
Lead, 
Copper, 
Mercury, 
Silver. 

Here  nitric  acid  (aquafortis)  is  placed  at  the  top  of  the  column,  and  under 
neath  it  are  some  of  the  metals  which  it  will  dissolve,  in  the  order  of  their 
affinity.  That  is,  the  nitric  acid  has  a  stronger  attraction  for  iron  than  for 
anyone  of  the  metals  below  it,  so  that  if  one  of  these  four  were  dissolved  in 
the  acid,  it  would  be  precipitated  by  the  iron.  In  like  manner  lead  would 
precipitate  the  three  placed  below  it. 

Again,  suppose  the  silver,  which  has  the  weakest  affinity  for  the  acid,  to 
be  dissolved  by  it;  if  we  then  put  some  mercury  into  the  solution,  this 
would  be  dissolved  and  the  silver  thrown  down.  Were  we  then  to  put  in  a 
piece  of  copper,  that  would  be  dissolved  and  the  mercury  precipitated;  and 
in  like  manner  the  other  metals  would  precipitate  each  other  in  their  regu- 
lar order;  but  neither  of  the  upper  metals  would  be  affected  by  these 
below  it(62). 

Tables  of  this  kind  are  denominated  tables  of  simple  affinity,  and  they 
are,  as  you  must  perceive,  of  great  use  to  the  chemist. 


60.  The  term  elective  attraction  is  frequently  used;  what  is  intended 
by  it? 

61.  What  means  have  been  devised  for  aiding  our  inquiries  on  elective 
attraction  ? 

62.  Explain  the  nature  of  the  example  given. 


ON  IMPONDERABLE  AGENTS.  23 

CONVERSATION  II. 

ON  IMPONDERABLE  AGENTS. 

Chemical  Jlgents  divided  into  Ponderable  and  Imponderable.  Light  and 
Heat  capable  of  separation.  Chemical  effects  of  Light.  Combination  -with 
compound  bodies.  Phosphorescence.  Caloric.  Heat,  its  sources.  Free 
and  combined  Caloric.  Tendency  of  Heat  to  Equilibrium.  Slow  Commit" 
nication  and  Radiation.  Good  and  bad  Conductors. 

Jlfrs  B.  Our  last  conversation  has  introduced  you  to  some  acquaintance 
with  the  general  principles  of  chemistry,  and  with  that  species  of  attraction, 
hy  which  substances,  differing  in  their  nature,  are  induced  to  combine  to- 
gether, and  form  a  third  body,  possessing  new  properties.  We  now  leave 
the  subject  of  chemical  attraction,  or  affinity,  for  a  short  period;  but  must 
not  finally  dismiss  it  without  some  addition  to  the  general  observations  which 
have  already  been  made.  You  will  be  better  preparexl  to  resume  it  after 
you  have  acquired  some  knowledge  of  the  particular  properties  of  a  few  of 
the  most  important  substances  in  their  simple  forms,  and  with  those  agents 
which  the  chemist  denominates  imponderable;  for  besides  the  division  of 
bodies  into  simple  and  compound,  the  objects  of  chemical  inquiry  are 
further  divided  into  ponderable  and  imponderable,  or  such  as  are  capable 
of  being  weighed,  and  such  as  do  not  appear  to  possess  any  weight(l). 

Caroline.  That  appears  to  me  to  be  a  strange  division.  I  thought  that  all 
matter  was  ponderable,  and  that  one  of  its  universal  attributes  was  gravita- 
tion; but  it  seems  that  in  learning  chemistry  we  must  forget  our  natural 
philosophy,  and  invest  matter  with  new  and  contradictory  properties.  Can 
there  be  such  a  thing  as  matter  without  weight? 

JWrs  B.  Your  remarks  are  certainly  acute,  but  still  you  appear  to  be  a 
little  too  ardent.  Of  one  thing  you  may  be  assured,  that  any  seeming  contra- 
diction in  the  laws  of  nature  serves  only  to  prove  the  imperfection  of  our 
own  knowledge.  The  imponderable  agents  are  light,  heat,  and  electri- 
city, including  galvanism  and  magnetism(2).  We  denominate  them  impon- 
derable, not  because  we  are  certain  that  they  are  without  weight,  but  sim- 
ply because  we  are  not  able  to  weigh  them(3);  just  as  we  call  a  body 
simple,  because  it  has  not  been  decomposed. 

Emily.  Is  it  not  possible  that  these  imponderable  bodies  may,  in  fact, 
be  no  bodies  at  all,  but  something  quite  distinct  from  common  matter,  in 
which  case  it  would  not  be  at  all  surprising  that  we  could  not  weigh  them? 

•Mrs  B.  I  have  used  the  term  agents,  because  some  philosophers  are  of 
opinion  that  the  imponderables  are  not  really  matter  itself,  but  like 
motion,  merely  properties  of  matter(4).  They  cannot  be  collected  to- 
gether, confined,  and  exhibited  in  masses  like  ponderable  matter:  and  hence 
the  phenomena  which  they  present  have  been  supposed  to  result  from 
certain  vibratory  motions  amongst  the  particles  of  bodies(5).  In  many  res- 


1.  The  objects  of  chemical  inquiry  are  divided  into  two  classes  other 
than  simple  and  compound,  what  are  they  ? 

2.  Name  the  imponderable  agents. 

3.  Do  we  know  that  they  are  absolutely  imponderable  ? 

4.  Why  is  the  term  agents  applied  to  them  ? 

5.  la  what  way  have  they  been  supposed  to  act  ? 


24  CONVERSATIONS  ON  CHEMISTRY. 

pects,  however,  they  exhibit  properties  and  produce  effects  so  analogous  to 
those  of  matter  in  general,  that,  disregarding  theoretical  opinions,  we  may 
safely  consider  them  as  material,  although  extremely  subtile,  and  apply  to 
them  the  same  language  which  we  use  in  treating  of  other  agents(6).  I 
shall  begin  withLiGHT,  and  then  pass  to  the  subject  of  heat,  with  which  it  is 
most  intimately  connected. 

Caroline.  1  recollect  that,  in  our  natural  philosophy,  light  was  spoken 
of  as  a  substance  which  emanated  from  the  sun  and  all  other  luminous  bo- 
dies, being  projected  from  them  with  prodigious  velocity,  in  particles  of 
extreme  minuteness(7);  and  it  has  always  appeared  to  me  that  the  same 
might  be  said  of  heat,  or  rather  that  light  and  heat  were  the  same  thing, 
only  affecting  different  senses. 

Jlfrs  B.  Whether  light  and  heat  be  altogether  different  agents,  or  not, 
I  cannot  pretend  to  decide;  but,  in  many  cases,  light  may  be  separated  from 
heat(8).  The  first  discovery  of  this  fact  was  made  by  a  celebrated  Swedish 
chemist,  named  Scheele.  Another  very  striking  illustration  of  the  separation 
of  heat  and  light  was  long  after  pointed  out  by  Dr  Herschel,  whose  experi- 
ments were  published  in  the  year  1800(9).  This  philosopher  discovered  that 
these  two  agents,  though  emitted  together  in  the  rays  of  the  sun,  are  not  equally 
refrangible,  but  that  heat  was  less  so  than  light;  for,  in  separating  the  different 
coloured  rays  of  li^ht  by  a  prism  (as  we  did  some  time  ago, )  he  found  that  the 
greatest  heat  was  out  of  the  spectrum,  at  a  little  distance  beyond  the  red 
rays,  which,  you  may  recollect,  are  the  least  refrangible.  Where 
there  is  no  light  whatever,  therefore,  we  find  the  greatest  heat;  and 
throughout  the  whole  of  the  spectrum,  the  illuminating  and  heating  ef- 
fects of  the  rays  bear  a  different  proportion  to  each  other(lO).  Although 
the  heat  is  refracted  as  well  as  the  light,  yet,  from  its  being  less  refrangible, 
the  heating  power  of  each  ray  decreases  as  you  approach  the  extreme 
violet. 

Emily.     I  should  like  to  try  that  experiment. 

Mrs  JB.  It  is  by  no  means  an  eusy  one:  the  heat  of  a  ray  of  light,  re- 
fracted by  a  prism,  is  so  small,  that  it  requires  a  very  delicate  thermometer 
to  distinguish  the  difference  of  the  degrees  of  heat  within  and  without  the 
spectrum.  For  in  this  experiment  the  heat  is  not  totally  separated  from 
the  light,  each  coloured  ray  retaining  a  certain  portion  of  it,  though  a  great 
part  is  not  sufficiently  refracted  to  fall  within  the  spectrum(ll). 

There  is,  however,  a  very  striking  experiment  in  proof  of  the  separability 
of  heat  and  light,  which  you  may  very  easily  try.  If  you  take  a  perfectly 
clear  pane  of  glass,  it  will  allow  the  rays  of  light  to  pass  through  with  very 
little  diminution  of  their  intensity;  yet  such  a  glass  will  arrest  nearly  the 
whole  of  the  radiant  heat.  To  prove  this,  place  your  face  near  to  the  fire, 
then  suddenly  interpose  the  glass  between  the  two,  and  although  the  light 
will  not  be  sensibly  obscured,  the  heat  will  appear  to  be  entirely  arrested(12)> 

Emily.  But  what  becomes  of  the  heat  in  this  case;  is  it  reflected  back 
again  by  the  glass  into  the  fire? 

Mrs  JB.     By  no  means,  it  is  absorbed  by  the  glass,  which,  consequently, 


6.  What  reason  is  assigned  for  treating  them  as  matter  ? 

7.  How  is  light  treated  of  in  natural  philosophy  ? 

8.  What  is  said  respecting  the  connexion  between  Tight  and  heat? 

9.  To  whom  are  we  particularly  indebted  for  experiments  on  this  sub- 
ject ? 

10.  What  particular  facts  are  mentioned  ? 

11.  What  difficulty  is  there  in  the  experiment? 

12.  How  is  the  general  fact  easily  proved? 


ON  LIGHT.  25 

becomes  rapidly  heated,  and  will  soon  begin  to  give  out  the  heat  which 
it  has  acquired,  as  you  will  find  by  continuing  it  in  its  situation(lS). 

Caroline.  It  certainly  appears,  very  plainly,  that  light  and  heat  can  be 
separated  from  each  other,  but  may  they  not,  after  all,  be  essentially  the 
same  ?  for  light,  which  you  call  a  simple  body,  may  be  divided  into  rays 
variously  coloured.  It  is  not  clear  to  me,  therefore,  that  heat  is  not  merely 
a  modification  of  light. 

Mrs  B.  That  is  a  supposition  which,  in  the  present  state  of  natural 
philosophy,  can  neither  be  positively  affirmed  nor  denied..  Let  us,  there- 
fore, instead  of  discussing  theoretical  points,  be  contented  with  examining 
what  is  known  respecting  the  chemical  effects  of  Iight(l4). 

Light  is  an  agent  capable  of  producing  various  chemical  changes.  It  is 
essential  to  the  welfare  both  of  the  animal  and  vegetable  kingdoms;  for  men 
and  plants  grow  pale  and  sickly  if  deprived  of  its  salutary  influence.  It  is 
likewise  remarkable  for  its  property  of  destroying  colour,  which  renders  it 
of  great  consequence  in  the  process  of  bleaching(15). 

Emily.  Is  it  not  singular  that  light,  which  in  studying  optics  we  were 
taught  to  consider  as  the  source  and  origin  of  colours,  should  have  also  the 
power  of  destroying  them? 

Caroline.  It  is  a  fact,  however,  which  we  every  day  experience;  you 
know  how  it  fades  the  colours  of  linens  and  silks(16). 

Emily.  Certainly.  And  I  recollect  that  endive  and  celery  are  made 
to  grow  white  instead  of  green,  by  being  covered  up  so  as  to  exclude  the  light. 
But  by  what  means  does  light  produce  these  effects(17)? 

Mrs  JB.  This  I  cannot  attempt  to  explain  to  you  until  you  have  obtain- 
ed a  further  knowledge  of  chemistry;  for  the  chemical  properties  of  light 
can  be  accounted  for  only  in  its  relationship  to  compound  bodies,  of  whixjh 
bodies  we  shall,  in  the  greater  number  of  instances,  find  light  to  form  a  con- 
stituent part,  and  that  it  is  frequently  given  out  during  their  decomposi- 
tion(18). 

Emily.  I  should  like  very  much  to  see  a  body  decomposed,  and  the  light 
given  out  from  it;  can  you  show  us  any  experiment  of  this  kind? 

Mrs  JB.  It  is  an  experiment  of  this  kind  which  now  enables  you  to  see 
me  and  all  the  articles  in  the  room;  and  you  witness  such  decompositions 
every  night  of  your  life. 

Caroline.  Thank  you  Mrs  B.  for  the  hint;  and  now  let  me  try  if  I  can- 
not explain  the  fact  to  which  you  allude.  Light,  I  suppose,  forms  one  of 
the  constituents  of  tallow  and  oil,  which  are  decomposed  in  burning,  and 
the  light  given  out(19). 

Mrs  B.  Very  good,  indeed;  your  explanation,  so  far  as  it  goes,  is  com- 
plete. The  light  given  out  by  burning  bodies,  or  by  those  which  are 
strongly  heated,  is  called  artificial  light;  whilst  that  given  out  by  the  sun, 
and  stars  is  called  natural  light.  These  two  kinds  of  light  differ  suffi- 
ciently, particularly  in  their  chemical  properties,  to  render  it  proper  to 
distinguish  them  from  each  other,  and  to  recollect  that,  in  general,  when  we 
speak  of  the  influence  of  light,  we  mean  natural  light — light  as  it  comes  to 
us  in  the  solar  ray(20). 


13.  What  becomes  of  the  heat? 

14.  Is  it  certain  that  light  and  heat  are  essentially  distinct? 

15.  Enumerate  some  of  the  chemical  effects  of  light 

16.  Give  examples  of  the  bleaching  property  of  light. 

17.  Does  its  exclusion  ever  render  bodies  white? 

IS.  What  is  said  respecting  light  and  some  compound  bodies? 

19.  Whence  comes  the  light  in  the  burning  of  candles,  &c.  ? 

20.  What  particular  distinction  is  mentioned  respecting  light? 

C 


26  CONVERSATIONS  ON  CHEMISTRY. 

Emily.  I  should  be  glad  to  know  some  particulars  in  which  these  two 
kinds  of  lig-ht  differ  from  each  other;  I  should  have  thought  that  they  were 
the  same,  excepting  in  their  intensity. 

Mrs  B.  The  differences  between  them  belong,  in  general,  to  a  more 
advanced  stage  of  our  subject,  and  we  must  anticipate  as  little  as  possible* 
There  is  one  point  of  difference,  however,  which  may  be  shown  by  this 
simple  pane  of  glass.  When  the  rays  of  light  and  heat  from  an  artificial 
source  met  the  glass,  you  found  that  but  little  of  the  heat  passed  through 
it;  but,  in  the  solar  ray,  nearly  the  whole  of  the  heat  accompanies  the 
light  in  its  transmission  through  it(21). 

Caroline.  It  seems  to  me  that  there  must  be  some  other  source  of  natu- 
ral light  besides  the  sun  and  stars,  as  there  are  some  substances  which 
always  shine  in  the  dark. 

Jlfrs  B.  Light  is  capable  of  entering  into  a  kind  of  transitory  union  with 
certain  substances,  and  thus  giving  to  them  what  has  been  called  phos- 
phorescence. Bodies  that  are  possessed  of  this  property,  will,  after  being  ex- 
posed to  the  sun's  rays,  appear  luminous  in  the  dark.  The  shells  of  fish, 
the  bones  of  land  animals,  marble,  limestone,  and  a  variety  of  combina- 
tions of  earths,  are  more  or  less  phosphorescent(22). 

Emily.  I  remember  being  much  surprised  last  summer  with  the  phos- 
phorescent appearance  of  some  pieces  of  rotten  wood,  which  had  just  been 
dug  out  of  the  ground:  they  shone  so  brightly  as  to  appear  to  be  actually  on 
flre.  The  light  of  the  fire-fly,  I  suppose,  is  also  of  a  phosphorescent  nature. 

JMrs  B.  It  is  a  very  remarkable  instance  of  phosphorescence  in  living 
animals.  This  property,  however,  is  not  exclusively  possessed  by  the  fire-fly. 
There  are  in  the  West  Indies,  and  in  South  America,  some  larger  insects 
which  emit  a  light  so  brilliant,  that  three  or  four  of  them  will  suffice  to 
enable  a  person  to  read  in  a  place  otherwise  dark(23). 

Emily.  But  is  it  certain  that  in  all  cases  of  phosphorescence  the  light 
proceeds  from  the  same  cause?  The  difference  between  a  piece  of  dead 
wood  and  a  living  animal  is  so  great  as  to  make  it  difficult  to  believe  this. 

J\frs  B.  It  certainly  is  not  probable  that  the  cause  is  the  same,  although 
there  is  a  similarity  in  the  results.  Dead  animal  matter  frequently  emits 
light,  and  this,  it  is  probable,  is  a  consequence  of  its  decomposition,  and 
may  therefore  be  analogous  to  that  given  out  in  combustion(24). 

Emily.  I  have  heard  that  the  sea  has  sometimes  the  appearance  of  being 
illuminated,  and  that  the  light  is  supposed  to  proceed  from  the  spawn  of 
fishes  floating  on  its  surface. 

•Mrs  B.  This  light  is  probably  owing  to  that  or  some  other  animal  mat- 
ter. Sea  water  has  been  observed  to  become  luminous  from  the  substance 
of  a  fresh  herring  having  been  immersed  in  it;  and  certain  insects,  of  the 
Medusa  kind,  are  known  to  produce  similar  effects.  There,  in  fact,  appear 
to  be  several  different  sources  of  the  luminousness  of  the  ocean(25). 

But  the  strongest  phosphorescence  is  produced  by  certain  chemical  com- 
positions prepared  for  the  purpose,  and  called  solar  phosphor!,  the  most 
common  of  which  consists  of  oyster-shells  and  sulphur,  calcined  together  in 
a  crucible;  this  kind  is  known  by  the  name  of  Canton's  phosphorus. 

To  cause  any  of  the  solar  phosphori  to  appear  luminous,  they  are  put 
into  a  well  stopped  phial,  and  after  being  exposed  to  the  direct  light  of  the 
sun,  they  shine  in  the  dark  for  some  minutes  with  a  brilliancy  sufficient  to 


21.  Give  an  evidence  of  the  difference  in  the  two. 

22.  Give  examples  of  phosphorescence. 

23.  What  is  noticed  respecting  phosphorescence  in  insects? 

24.  Is  it  probable  that  this  light  is  always  produced  in  the  same  way? 

25.  What  is  said  respecting  the  luminous  appearance  of  the  sea? 


ON  HEAT,  OR  CALORIC.  27 

show  the  time  by  a  watch.  By  degrees  they  cease  to  shine,  hut  again  do  so 
as  often  as  they  are  exposed  to  the  light(26). 

Caroline.  Light,  in  this  case,  appears  to  operate  very  much  like  heat. 
If  I  warm  a  body  and  remove  it  to  a  cool  place,  the  heat  will  pass  off,  and 
this  I  can  repeat  again  and  again. 

Mrs  B.  There  is  certainly  a  striking  resemblance  between  the  two  in  this 
particular,  and  it  has  been  used  as  an  argument  by  those  who  do  not  believe 
heat  and  light  to  be  distinct  material  substances.  The  particles  of  light 
seem  to  adhere  to  these  phosphori  with  a  certain  degree  of  force,  and  gradu- 
ally to  fly  off,  and,  as  it  were,  to  evaporate(27).  But  it  is  time  for  us  to  pass 
on  to  the  examination  of  heat,  or  caloric,  which,  as  it  is  the  most  powerful 
of  all  the  chemical  agents,  will  demand  a  considerable  share  of  attention. 

HEAT  and  LIGHT  may  be  always  distinguished  by  the  different  sensations 
they  produce.  Light  affects  the  sense  of  sight;  heat,  or  caloric,  that  of 
feeling;  the  one  produces  vision,  the  other  the  sensation  of  warm*A(28). 

Caroline.  It  seems  to  me  quite  unnecessary  and  embarrassing  to  call  the 
same  thing  by  two  names;  and  this  is  evidently  the  case  with  the  chemists 
who  have  introduced  the  term  caloric,  which  you  have  just  used  as  synony- 
mous with  heat(29). 

Mrs  JB.  You  are,  in  the  present  instance,  both  too  prompt  and  too  con- 
fident in  your  judgment.  The  term  caloric  was  introduced,  because  philo- 
sophers, as  well  as  the  vulgar,  were  in  the  habit  of  calling  two  distinct 
things  by  the  same  name. 

The  cause,  calorie,  and  the  effect,  heat,  were  confounded  together  under 
the  same  denomination,  whilst  they  are,  in  fact,  as  distinct  and  different 
from  each  other  as  are  light  and  vision(SO).  Although  this  distinction  has 
been  made,  the  chemist  frequently  departs  from  its  strict  observance,  often 
using  the  word  heat  to  designate  the  operating  agent,  as  well  as  the  effect 
which  it  produces.  In  conformity  with  universal  custom,  also,  we  speak 
of  the  heat  of  inanimate  matter,  as  ihe  heat  of  an  oven,  or  the  heat  of  the 
sun,  without  any  reference  to  the  sensation  which  it  is  capable  of  exciting(Sl). 
Caloric,  you  will  hereafter  find,  may  exist  in  a  body  without  increasing  its 
temperature,  and  of  course  it  is  in  such  a  case  imperceptible  to  us(32). 

Emily.  It  must  be  a  very  strange  kind  of  heat  that  cannot  be  perceived 
by  our  senses,  which  seem  to  be  the  only  means  by  which  we  know  of  its 
existence. 

Mrs  B.  Light  has  been  spoken  of  as  combining  with  bodies,  and  form- 
ing a  part  of  their  substance;  and  whilst  in  this  state,  its  pewer  of  exciting 
vision  is  suspended.  In  like  manner  heat  may  combine  with,  and  form  part 
of  a  compound;  and  whilst  so  combined,  it  will  not  excite  any  sensation  in 
us(33).  If  I  touch  a  "warm  body,  it  is  the  caloric  which  passes  from  that 
body  into  my  hand  which  produces  the  sensation  of  warmth;  if  the  caloric 
were  combined  with,  and  did  not  leave  the  body,  it  would  not  produce  any 
effect  upon  me(34). 

Caroline.  There  are,  therefore,  two  entirely  different  modifications  of 
caloric;  one  in  which  it  produces  heat,  and  another  hi  which  it  does  not. 


26.  What  of  solar  phosphori? 

27.  What  analogy  is  noticed  between  light  and  heat? 

28.  By  what  properties  are  light  and  heat  distinguished? 

29.  What  term  is  used  by  the  chemist  as  synonymous  with  heat? 

30.  What  distinction  exists  strictly  between  caloric  and  heat? 

31.  Is  this  distinction  always  observed? 

32.  What  is  said  of  caloric,  without  heat? 

33.  What  analogy  is  there  between  light  and  heat  in  this  particular? " 

34.  How  does  a  warm  body  produce  the  sensation  of  heat? 


28  CONVERSATIONS  ON  CtfEMISTRY. 

Mrs  B.  We  are  acquainted  with  three  distinct  sources  of  heat.  The  sun 
you  know  as  the  great  and  principal  source;  but  we  also  derive  it  from  me- 
chanical and  from  chemical  action.  Friction,  or  the  rubbing  of  two  solid 
bodies  together,  and  percussion,  are  examples  of  the  former,  and  combustion 
is  a  familiar  one  of  the  latter(35). 

Caloric  is  found  also  to  exist  under  a  variety  of  forms  or  modifications; 
your  attention,  however,  will  be  directed  to  it  under  the  two  principal, 
which  are 

1.  FREE  or  RADIANT  CALORIC, 

2.  COMBINED  CALORIC,  called  also  LATENT  HEAT(36). 

The  first,  FREE  OR  RADIANT  CALORIC,  is  also  called  SENSIBLE  HEAT,  or 
HEAT  OF  TEMPERATURE;  it  comprehends  all  heat  which  is  perceptible  to 
the  senses,  and  affects  the  thermometer. 

Emily.  You  mean  such  as  the  heat  of  the  sun,  of  fire,  of  candles,  of 
stoves;  in  short,  of  every  thing  that  burns? 

Mrs  B.  And  likewise  of  things  that  do  not  burn,  as,  for  instance,  the 
warmth  of  the  body;  in  a  word,  all  heat  that  is  sensible,  whatever  may  be  its 
degree,  or  the  source  from  which  it  is  derived(37). 

In  examining  into  these  modifications,  we  shall  consider  heat  or  caloric 
as  material,  and  capable  of  inciease  or  diminution  in  a  body(38).  This 
being  admitted,  it  will  appear  to  be  a  subtile  fluid,  the  particles  of  which 
repel  each  other,  and  are  attracted  by  all  ponderable  substances;  and  that 
it  is  present  in  all  bodies,  however  low  their  temperature(39).  That  the 
last  is  a  fact,  you  can  readily  conceive;  as  it  is  easy  to  imagine  the  tem- 
perature of  a  body  to  be  reduced  still  lower  than  it  is,  which  could  take 
place  only  by  its  parting  with  caloric(40). 

Caroline.  I  am  quite  impatient  to  learn  every  thing  respecting  your 
second  modification;  as  to  sensible  heat,  it  already  seems  to  be  familiar  to 
me,  but  your  insensible  caloric  is  quite  a  new  subject. 

Mrs  B.  I  thought  we  were  to  proceed  methodically; 'if  we  do  not,  you 
will  soon  become  involved  in  a  labyrinth,  whence  you  will  scarcely  be  able 
to  extricate  yourselves.  On  the  subject  of  free  caloric,  or  sensible  heat, 
you  have  much  to  learn.  Your  attention  will  be  directed,  1st,  to  the  uni- 
versal tendency  of  free  caloric  to  an  equilibrium;  2d,  to  the  manner  in 
•which  this  tendency  is  exerted;  and  3d,  to  the  effects  produced  upon  bodies 
by  its  entrance  into  them(4l). 

Emily.  The  first  division  seems  to  include  a  contradiction  of  known 
facts,  for  if  there  be  a  constant  tendency  in  all  bodies  to  the  same  tempera- 
ture, it  seems  to  me  that  they  must  have  long  since  arrived  at  it. 

Mrs  B.  Your  remark  is  specious,  but  not  solid.  Water  has  a  constant 
tendency  to  find  its  level,  yet  there  is  a  perpetual  flux  and  reflux  of  the 
tides  in  the  sea,  and  in  rivers,  because  there  are  disturbing  causes  which 
counteract  this  tendency;  and  the  same  is  the  case  with  heat.  The  sun 
supplies  his  rays  by  day,  and  they  are  withdrawn  at  night;  clouds,  winds, 
rain,  and  a  thousand  mechanical  and  chemical  changes  alter  the  temperature 
of  bodies;  you  are  familiar  with  this  fact  in  combustion,  and  will  hereafter 
become  acquainted  with  it  in  numerous  other  instances(42).  This  ten- 


35.  What  are  the  three  sources  of  heat? 

36.  What  are  the  two  principal  modifications  of  caloric? 

37.  What  is  said  of  free  or  radiant  heat? 

38.  How  is  heat  considered,  inregard  to  its  nature,  in  these  conversations? 

39.  What  kind  of  fluid  will  it  then  appear  to  be? 

40.  What  may  we  suppose  to  justify  the  last  conclusion? 

41.  The  subject  of  free  caloric  is  treated  under  three  heads,  name  them. 

42.  What  prevents  au  actual  equilibrium  of  temperature? 


ON  FREE  CALORIC.  29 

dency  to  an  equilibrium  serves  to  correct  these  disturbing  causes,  and  both 
co-operate  in  producing  and  perpetuating  that  harmonious  variety  which  so 
delightfully  diversifies  our  days  and  our  seasons(43). 

Caroline.  But  if  this  equilibrium  is  never  attained,  I  do  not  see  how  we 
can  infer  the  universal  prevalence  of  a  tendency  towards  it.  Water  seeks  its 
level  because  it  gravitates,  but  caloric  is  imponderable,  and  therefore  is  with- 
out that  property  which  actuates  water,  in  the  tendency  of  which  we  are 
speaking(44). 

Jlfrs  B.  Very  true,  Caroline,  that  is  an  excellent  objection.  You 
might  also,  with  some  propriety,  object  to  the  term  equilibrium  being  ap- 
plied to  a  body  that  is  without  weight;  but  I  know  of  no  expression  that 
would  explain  my  meaning  so  well.  You  must  understand  it,  however,  in  a 
figurative  rather  than  a  literal  sense:  its  strict  meaning  is  an  equal  dijfu- 
«j'on(45).  We  have  already  considered  the  particles  of  caloric  as  repulsive  of 
each  other,  and  as  attracted  by  other  bodies,  and  these  properties  may  afford 
us  some  light  upon  the  subject  we  are  considering.  Where  there  is  most  ca- 
loric there  will  be  most  repulsion,  and  of  course  the  caloric  of  a  warmer 
body  must,  by  this  repulsion,  be  disposed  to  leave  that  body  and  unite  with  a 
colder.  The  proofs  of  this  tendency  are  numerous  and  complete(46).  If  we 
place  a  hot  piece  of  iron  in  contact  with  one  that  is  cold,  the  former  will  ra- 
pidly lose,  and  the  latter  acquire  heat,  and  in  a  short  period  they  will  both 
have  arrived  at  the  same  temperature.  If  a  number  of  substances,  different 
in  temperature,  be  enclosed  in  an  apartment  in  which  there  is  no  actual 
source  of  caloric,  they  will  very  soon  acquire  an  equilibrium,  so  that  a 
thermometer  placed  in  contact  with  either  of  them  will  indicate  the  same 
temperature(47). 

Emily.  Although  I  have  no  doubt  of  the  fact,  I  am  at  a  loss  to  perceive 
how  this  equilibrium  is  produced,  especially  when  the  warm  and  the  cold 
bodies  are  at  a  distance  from  each  other. 

JUrs  B.  Heat  passes  from  one  body  to  another  in  two  ways:  first,  by 
what  is  sometimes  called  the  slow  communication,  or  conducting  power,  and 
second,  by  radiation,  or  rapid  communication(48).  When  bodies  of  differ- 
ent temperatures  are  in  contact  with  each  other,  it  is  conducted  from  one  to 
the  other}  when  they  are  placed  at  a  distance,  it  is  radiated.  If  you  place 
your  hand  upon  a  heated  body,  the  former  takes  place;  if  you  stand  before 
the  fire,  or  in  the  sunshine,  you  receive  heat  by  radiation.  These  two 
causes  constantly  operate  in  diffusing  caloric.  Thus  the  fire  which  burns 
in  the  grate,  communicates  its  heat  from  one  object  to  another,  till  every 
part  of  the  room  has  a  portion  of  it(49). 

Emily.  And  yet  this  book  is  not  so  cold  as  the  table  on  which  it  lies, 
though  both  are  at  an  equal  distance  from  the  fire,  and  actually  in  contact  with 
each  other;  but  according  to  your  theory,  they  should  be  exactly  at  the 
same  temperature. 

Caroline.  And  the  hearth,  which  is  much  nearer  the  fire  than  the  carpet, 
is  certainly  the  colder  of  the  t*vo(50). 

JMrs  B.     If  you  ascertain  the  temperature  of  these  several  bodies  by  a 


43.  What  benefits  result  from  this  tendency  ^ 

44.  What  objection  is  urged? 

45.  What  to  the  term  equilibrium? 

46.  How  is  the  tendency  to  equal  diffusion  exerted? 

47.  Give  the  examples. 

48.  By  what  two  means  is  heat  diffused? 

49.  Give  the  exemplifications. 

50.  What  objection  is  urged? 

C  0, 


30  CONVERSATIONS  ON  CHEMISTRY. 

thermometer  (which  is  a  much  more  accurate  test  than  your  feeling,)  you 
•will  find  that  it  is  exactly  the  same  in  all(51). 

Caroline.  But  if  they  are  of  the  same  temperature,  why  should  the  one 
feel  colder  than  the  other  ? 

Jlfrs  B.  The  hearth  and  the  table  feel  colder  than  the  carpet  or  the 
hook,  hecause  the  latter  are  not  such  good  conductors  of  heat  as  the  former. 
Caloric  finds  a  more  easy  passage  through  marble  and  wood,  than  through 
leather  and  worsted;  the  two  former  will  therefore  absorb  heat  more  ra- 
pidly from  your  hand,  and  consequently  give  it  a  stronger  sensation  of  cold 
than  the  two  latter,  although  they  are  all  of  them  really  of  the  same  tem- 
perature(52). 

Caroline.  So,  then,  the  sensation  I  feel  on  touching  a  cold  body,  is  in 
proportion  to  the  rapidity  with  which  my  hand  yields  its  heat  to  that  body. 

Mrs  B.  Precisely;  and  if  you  lay  your  hand  successively  on  every  ob- 
ject in  the  room,  you  will  discover  which  are  good,  and  which  are  bad  con- 
ductors of  heat,  by  the  different  degrees  of  cold  which  you  feel.  But  in 
order  to  ascertain  this  point,  it  is  necessary  that  the  several  substances 
should  be  of  one  uniform  temperature,  which  will  not  be  the  case  with 
those  that  are  very  near  the  fire,  or  those  that  are  exposed  to  a  current  of 
cold  air  from  a  window  or  door(53). 

Emily.  But  what  is  the  reason  that  some  bodies  'are  better  conductors 
of  heat  than  others  ? 

Mrs  B.  That  is  a  point  not  well  ascertained.  In  general  the  most 
dense  bodies,  as  the  metals,  are  the  best  conductors,  whilst  those  which 
are  light  and  porous  are  bad  conductors;  and  this  undoubtedly  arises,  in 
part,  from  the  points  of  contact  being  more  numerous  in  dense  bodies  than 
in  those  that  are  more  rare.  From  this  cause  iron  filings  conduct  heat 
more  slowly  than  the  solid  metal.  This,  however,  is  not  the  sole  cause,  as 
the  conducting  power  is  not  always  proportioned  to  the  density(54). 

Whatever  may  be  the  causes  which  operate  in  producing  this  difference 
in  conducting  power,  you  now  clearly  understand,  that  the  passage  of  calo- 
ric through  bodies  that  are  good  conductors,  is  much  more  rapid  than, 
through  those  that  are  bad  conductors;  and  that  the  former  both  give  and 
receive  it  more  quickly,  and  therefore  in  a  given  time  more  abundantly, 
than  bad  conductors,  which  makes  them  feel  either  hotter  or  colder,  though 
they  may,  in  fact,  both  be  of  the  same  temperature. 

Caroline.  Yes,  I  understand  it  now;  the  table  and  the  book  lying  upon 
it,  being  really  of  the  same  temperature,  would  each  receive  in  the  same 
space  of  time,  the  same  quantity  of  heat  from  my  hand,  were  their  conduct- 
ing powers  equal;  but  as  the  table  is  the  host  conductor  of  the  two,  it  will 
absord  the  heat  from  my  hand  more  rapidly,  and  consequently  produce  a 
stronger  sensation  of  cold  than  the  book,  as  it  is  the  heat  which  my  hand 
loses  that  causes  it  to  feel  cold(55). 

Mrs  B.  Very  well,  my  dear;  and  observe,  likewise,  that  if  you  were  to 
heat  the  table  and  the  book  an  equal  number  of  degrees  above  the  tempera- 
ture of  your  bodyf  the  table,  which  before  felt  the  colder,  would  now  feel 
the  hotter  of  the  two;  for,  as  in  the  first  case  it  took  the  heat  most  rapidly 
from  your  hand,  so  now  it  will  most  rapidly  impart  heat  to  it.  Thus  the 
marble  table,  which  seems  to  us  colder  than  the  mahogany  one,  will  prove 


51.  How  is  the  objection  removed? 

52.  Why  is  the  sensation  of  heat  different  from  bodies  of  the  same  tem- 
perature ? 

53.  How  may  good  and  bad  conductors  be  detected? 

54.  What  is  said  of  the  cause  of  this  difference? 

55.  Give  the  illustrations. 


ON  FREE  CALORIC.  31 

the  hotter  of  the  two  to  a  piece  of  ice  placed  upon  it;  for,  if  it  takes  heat  more 
rapidly  from  our  hands,  which  are  warmer  than  itself,  it  will  give  out  heat 
more  rapidly  to  the  ice,  which  is  colder.  Do  you  understand  the  reason 
of  these  apparently  opposite  effects(56)? 

Emily.  Perfectly.  A  body  which  is  a  good  conductor  of  caloric,  af- 
fords it  a  free  passage,  so  that  it  penetrates  through  that  body  more  rapidly 
than  through  one  which  is  a  bad  conductor;  consequently,  when  I  place  my 
hand  in  contact  with  a  good  conductor,  if  the  body  touched  be  colder  than 
the  hand,  it  loses  more  caloric,  in  a  given  time;  and  if  it  be  hotter,  gains 
more  than  it  would  do  were  the  substance  a  bad  conductor  and  at  the  same 
temperature(57). 

Mrs  B.  But  you  must  observe  that  this  is  the  case  only  when  the  con- 
ductors are  either  hotter  or  colder  than  your  hand:  for,  if  you  heat  different 
conductors  to  the  temperature  of  your  body,  they  will  all  feel  equally 
warm,  since  the  exchange  of  caloric  between  bodies  of  the  same  tempera- 
ture is  equal(58).  Now,  can  you  tell  me  why  flannel  clothing,  which  is  a 
very  bad  conductor  of  heat,  prevents  our  feeling  cold? 

Caroline.     It  prevents  the  cold  from  penetrating         « 

JMrs  B.  But  you  forget  that  cold  is  only  a  negative  quality;  we  do  not 
suppose  that  any  thing  more  is  requisite  to  cause  a  body  to  become  cold, 
than  merely  for  the  heat  to  pass  out  of  it. 

Caroline.  True,  it  only  prevents  the  heat  of  our  bodies  from  escaping  so 
rapidly  as  it  would  otherwise  do. 

Mrs  B.  You  have  explained  it  correctly;  the  flannel  rather  keeps  in 
the  heat  than  keeps  out  the  cold(59).  Were  the  atmosphere  of  a  higher 
temperature  than  our  bodies,  it  would  be  equally  efficacious  in  protect- 
ing them  against  an  increase  of  temperature,  as  it  would  prevent  the  free 
access  of  the  external  heat,  by  the  difficulty  with  which  it  conducts  it. 

Emily.  This,  I  think,  is  very  clear.  Heat,  whether  external  or  inter- 
nal, cannot  easily  penetrate  flannel;  therefore  in  cold  weather  it  keeps  us 
warm,  and  if  the  weather  were  hotter  than  our  bodies,  it  would  keep  us 
cool. 

Mrs  B.  You  now  perceive  the  reason  why  we  wrap  a\  heated  brick  or 
a  lump  of  ice  in  flannel,  to  cause  the  first  to  retain  its  heat,  and  to  pre- 
vent the  latter  from  thawing. 

Caroline.  O  yes,  that  I  understand  perfectly;  the  atmosphere  is  colder 
than  the  brick,  and  would  rob  it  of  its  heat,  but  it  is  warmer  than  the  ice, 
and  would  therefore  communicate  heat  to  it  and  so  cause  it  to  melt;  these 
effects  the  flannel  prevents,  by  keeping  the  heat  from  passing  outwards  from 
the  brick,  and  inwards  from  the  air  to  the  ipe(60). 

Mrs  B.  We  have  already  remarked  that  the  most  dense  bodies  are 
usually  the  best,  and  the  lighter  bodies  the  worst  conductors  of  caloric. 
Air,  which  has  but  little  density,  is  known  to  be  a  very  bad  conductor,  and 
this  is  undoubtedly  one  great  reason  why  light,  fibrous  materials,  such  as  flan- 
nel, fur  and  down  are  very  bad  conductors,  as  they  contain  a  con«iderable 
quantity  of  air  entangled  between  their  fibres.  Down,  which  is  the  lightest 
and  the  most  fibrous,  is  the  worst  conductor,  or,  as  you  would  say,  makes 
the  warmest  covering(Gl). 


56.  What  is  remarked  of  substances  heated  above  the  temperature  of  the 
body? 

57.  Give  Emily's  explanation. 

58.  What  is  the  operation  of  bodies  at  equal  temperatures? 

59.  How  does  flannel  operate  in  keeping  us  warm? 

60.  For  what  apparently  opposite  purposes  are  bad  conductors  used  ? 

61.  Why  are  light  fibrous  materials  bad  conductors? 


32  CONVERSATIONS  ON  CHEMISTRY. 

Caroline.  This  is,  I  suppose,  the  reason  why  the  plumage  of  birds  pre- 
serves them  so  effectually  from  the  influence  of  cold  in  winter? 

Mrs  B.  Yes;  feathers  in  general  are  an  excellent  preservative  against 
cold;  but  aquatic  birds  have  a  kind  of  plumage  peculiar  to  themselves,  co- 
vering their  breasts,  which  is  the  part  most  exposed  to  cold;  for  though  the 
surface  of  the  water  is  not  of  a  lower  temperature  than  the  atmosphere,  yet, 
as  this  fluid  is  a  better  conductor  of  heat,  it  feels  much  colder;  consequently 
the  breast  of  the  bird  requires  a  warmer  covering  than  the  upper  part  of  its 
body(62). 

Most  animal  substances,  especially  those  which  Providence  has  assigned 
to  them  as  a  covering,  such  as  fur,  wool,  hair,  silk,  &c.  are  bad  conduc- 
tors of  heat,  and  are,  on  that  account,  such  excellent  preservatives  against 
the  inclemency  of  winter,  that  our  warmest  apparel  is  made  of  these  ma- 
terial s(  63). 

Emily.  Wood  is,  I  dare  say,  not  so  good  a  conductor  as  metal,  and  it  is 
for  that  reason,  no  doubt,  that  silver  tea-pots  have  always  wooden  handles. 

Mrs  B.  You  are  correct,  and  as  is  the  case  in  the  fibrous  materials 
used  for  clothing,  it  is  probable  that  the  air  contained  in  the  pores  of  the 
wood  tends  much  to  lessen  its  conducting  power(64). 

Caroline.  It  is  a  very  fortunate  circumstance  that  air  should  be  a  bad 
conductor,  as  otherwise  the  heat  of  the  body,  when  exposed  to  cold 
weather,  would  be  rapidly  carried  off. 

Mrs  B.  This  is  one  of  the  many  benevolent  dispensations  of  Providence, 
in  order  to  soften  the  inclemency  of  the  seasons,  and  to  render  almost  all 
climates  habitable  to  man (65). 

The  power  of  conducting  heat  varies  likewise  very  remai-kably  in  fluids 
of  different  densities.  If  you  dip  your  hand  into  this  vessel  of  mercury, 
you  will  scarcely  be  able  to  conceive  that  its  temperature  is  not  lower  than 
that  of  the  atmosphere. 

Caroline.  Indeed  it  is  difficult  to  believe  that  it  is  not,  it  feels  so  ex- 
tremely cold.  But  we  may  easily  ascertain  its  true  temperature  by  the 
thermometer.  It  is  really  not  colder  than  the  air;  the  apparent  difference 
then  is  produced  merely  by  the  difference  of  the  conducting  power  in  mer- 
cury and  in  air(66). 

Mrs  B.  Yes;  and  hence  you  may  judge  how  little  the  sense  of  feeling  is 
to  be  relied  on  as  a  test  of  the  temperature  of  bodies,  and  how  necessary 
for  that  purpose  is  a  thermometer. 

To  show  you  the  fallacy  of  our  judgment  of  temperature  when  guided  by 
the  sense  of  feeling  alone,  I  have  placed  water  of  three  different  tempera- 
tures in  these  three  bowls;  that  to  your  left  contains  ice;  the  water  in  the 
one  to  your  right  is  heated  so  that  you  can  just  bear  to  hold  your  hand  in 
it,  and  that  in  the  middle  bowl  is  at  about  the  temperature  of  your  body. 
Now  hold  one  hand  in  the  hot,  and  the  other  in  the  iced  water  for  some 
time,  and  then  plunge  them  both  into  the  middle  bowl. 

Emily.  Oh!  To  my  left  hand  it  feels  as  if  the  water  was  very  much 
heated,  and  to  my  right,  like  the  iced  water.  One  hand  declares  it  to  be 
cold,  and  the  other  to  be  warm;  which  shall  I  believe(67)? 

Caroline.  Neither;  but  let  us  both  always  recollect,  that  we  are  endow- 
ed with  reason  as  well  as  with  sensation,  and  that  we  should  rarely  allow 


62.  What  is  remarked  respecting  aquatic  birds? 

63.  What  of  our  warmest  apparel? 

64.  What  respecting  wood? 

65.  What  respecting  air? 

66.  Give  the  exemplification  of  the  difference  in  fluids. 

67.  Relate  the  ex  leriment  with  three  bowls? 


FREE  CALORIC— CONDUCTING  POWER. 


33 


the  latter  to  guide  us  until  its  conclusions  are  sanctioned  by  the  former. 
This,  I  well  know,  is  a  lesson  which  I  very  much  need  to  learn(68). 

Since  we  are  now  so  fully  convinced  of  the  fallacy  of  the  sense  of  feel- 
ing in  ascertaining  the  real  temperature  of  a  body,  and  shall  be  compelled 
to  resort,  perpetually,  to  the  thermometer,  I  should  like  to  know  something 
more  than  I  do  respecting  the  principle  upon  which  that  instrument  acts. 

Mrs  E.  We  will  soon  attend  to  that,  but  you  are  not  yet  quite  prepared 
to  enter  upon  the  subject,  and  in  the  mean  time  you  can  advantageous- 
ly employ  the  thermometer,  as  you  know  that  the  rise  and  fall  of  the  mer- 
cury indicates  corresponding  changes  in  temperature.  We  have  not  yet 
done  with  the  conducting  power  of  bodies,  nor  have  we  examined  the  sub- 
ject of  radiation;  and  before  proceeding  further  you  will  do  well  to  rumi- 
nate upon  what  has  been  already  explained,  and  we  will  resume  its  further 
consideration  to-morrow.  '»/ 


CONVERSATION  III. 


FREE  CALORIC  CONTINUED. 

Difference  in  the  Conducting  Poioer  of  Bodies.  Fluids  the  -worst  Conduc- 
tors. Radiation  of  Caloric.  Pictet's  Experiments.  Radiating  Power  of 
different  surfaces.  Potoer  of  absorbing  different  in  different  surfaces. 
Distinction  between  Radiation  and  Reflection. 

Jlfrs  _B.  There  are  many  easy  and  striking  experi- 
ments which  manifest  the  difference  in  the  conducting 
power  of  different  solids;  after  attending  to  two  or  three 
of  these,  you  must  learn  something  of  the  manner  in 
which  heat  is  distributed  through  fluids. 

If  you  place  one  end  of  a  rod  of  iron  in  the  fire,  you 
will  find  that  the  heat  passes  with  comparative  quick- 
ness to  the  other  extremity,  whilst  a  piece  of  wood  of 
the  same  size  may  be  burnt  nearly  its  whole  length 
without  any  sensible  conveyance  of  heat  along  it(l)./ 

Here  is  a  pin  and  a  small  strip  of  glass  about  equal 
in  size  and  length;  now,  Emily,  take  these  together  in 
your  fingers  and  hold  one  end  of  each  in  the  flame  of  the 
candle. 

Emily.  See,  I  have  been  compelled  to  let  the  pin  fall; 
it  was  too  hot  to  hold,  yet  I  do  not  feel  the  glass  warm, 
although  the  end  in  the  flame  has  melted(2)! 

Jtfrs  £.  Because  glass  is  a  very  bad  conductor,  and 
the  metals  are  very  good  ones:  these  latter,  however, 
differ  greatly  from  each  other,  as  this  little  instrument 
will  show  you.  -''Small  bars  of  four  different  metals,  all 
of  equal  size,  are  attached  to  a  piece  of  brass,  which  may 
be  heated  by  holding  it  over  a  lamp  by  means  of  the 
handle,  and  the  metal  bars  will  of  course  become  heat- 
ed. These  bars  are  of  silver,  copper,  iron,  and  lead;  I 


68.  What  deduction  does  Caroline  draw? 

Vl.   Give  the  example  of  the  difference  in   the    conducting  powers   of 
iron  and  wood. 

2.  Give  that  of  glass  and  a  common  pin. 


_. 

34  CONVERSATIONS  ON  CHEMISTRY. 

have  dipped  each  of  them  into  melted  wax,  and  by  this  I  have  cemented 
a  piece  of  card  to  the  end  of  each.  We  shall  find  on  heating  them  that 
the  silver  is  the  best  conductor,  next  the  copper,  and  then  the  iron,  whilst  the 
lead  is  very  inferior  lo  either  of  the  others.  Observe  the  wax  is  melting 
first  upon  the  silver; — and  now  the  piece  of  card  has  fallen  from  it. 

Emily.  The  pieces  have  fallen  from  each  in  the  order  in  which  you 
named  them,  and  the  difference  between  them  has  proved  to  be  much  greater 
than  I  expccted(S). 

Mrs  JB.  You  have  seen  that  although  all  solids  are  conductors  of  heat, 
they  vary  greatly  from  each  other  in  this  respect.  In  speaking  of  air  it  was 
mentioned  as  a  very  bad  conductor,'  and  you  are  to  understand  the  same  of 
all  fluids,  v  «.ether  elastic  or  non-elastic(4).  That  distinguished  philosopher, 
Count  Rumford,  who  investigated  this  subject  with  much  care,  considered 
fluids  as  being  absolutely  non-conductors,  and  believed  that  if  their  particles 
could  be  kept  from  motion  among  themselves,  it  would  be  impossible  to 
heat  them  throughout(S). 

Caroline.  How  could  the  Count  think  so,  as  we  know  that  they  are  ca- 
pable of  imparting  heat  to,  or  taking  it  from  us,  accordingly  as  they  are 
hotter  or  colder  than  we  are? 

Emily.  And  how,  if  the  particles  of  water  do  not  communicate  heat  to 
each  other,  does  that  which  is  contained  in  a  vessel  over  the  fire  become 
hot  throughout(G)? 

Mrs  B.  Count  Rumford  admitted  that  solid  bodies  would  communicate 
heat  to  the  particles  of  fluids  which  were  in  contact  with  them,  and  that 
fluids  would  in  like  manner  communicate  it  to  solids,  but  denied  that 
any  such  interchange  took  place  between  the  particles  of  fluids  them- 
selves^). With  respect  to  Emily's  question,  the  particles  of  fluids,  you  know, 
move  with  the  most  perfect  facility  among  themselves,  and  you  are  also 
aware  that  fluids  are  expanded  by  heat,  and  consequently  rendered  specifi- 
cally lighter;  it  was  to  these  two  circumstances  that  the  Count  attributed 
the  diffusion  of  heat  in  fluids.  When  a  vessel  containing  water  is  placed 
upon  the  fire,  the  bottom  of  it  becomes  heated,  and  communicates 
its  heat  to  the  particles  of  water  in  contact  with  it;  these  becoming  ex- 
panded, and  consequently  lighter  than  the  portions  above,  rise  to  the  sur- 
face and  leave  a  new  layer  of  particles  to  be  acted  upon,  in  the  same  way. 
This  change  of  place  continues  until  the  whole  of  the  water  has  arrived  at 
the  boiling  point;  the  heat  not  being  communicated  from  particle  to  parti- 
cle, but  conveyed,  or  carried  by  the  currents  which  are  established(S). 

Caroline.  This  accounts  most  ingeniously  for  the  propagation  of  heat 
upwards;  but  supposing  you  were  to  heat  the  upper  surface  of  a  liquid,  the 
particles  being  specifically  lighter  than  those  below,  could  not  descend. 
How,  therefore,  would  the  heat  be  communicated  downwards? 

Mrs  Ji.  Had  the  Count's  assumption  been  absolutely  correct,  a  liquid 
could  not  be  heated  from  above(9);  and  indeed,  although  this  does  take 
place,  it  is  effected  so  slowly,  that  he  believed  the  heat  was,  in  every  case, 
conducted  down  by  the  solid  vessel  in  which  the  fluid  must  be  contained;  the 
effect  being  more  or  less  slow  as  this  is  a  good  or  bad  conductor(lO). 


3.  How  may  the  difference  in  the  conducting  power  of  metals  be  shown? 

4.  Are  fluids  good  conductors? 

5.  What  opinion  did  Count  Rumford  entertain  upon  this  point? 

6.  What  objections  are  urged  to  this  opinion  of  Rumford? 

7.  How  did  Rumford  suppose  heat  to  operate  between  solids  and  fluids? 

8.  In  what  way  did  he  suppose  that  heat  was  diffused  in  a  fluid? 

9.  Why  would  not  this  account  for  heat  descending  in  a  fluid? 
10.  How  did  Rumford  suppose  the  descent  to  be  effected? 


FREE  CALORIC— CONDUCTING  POWER. 


35 


It  is  certain  that  heat  is  diffused  in  liquids  principally  by  the  motion 
among  their  particles.  Although  this  motion  is  invisible  on  account  of  their 
extreme  minuteness,  we  can,  by  a  little  artifice,  manifest  the  existence 
of  the  currents  of  which  I  have  spoken.  If  you  mix  with  the  liquid  any 
coloured  dust,  or  powder,  of  nearly  the  same  specific  gravity  as  itself, 
you  may  judge  of  the  internal  motion  of  the  fluid  by  that  of  the  coloured 
dust  which  it  contains.  Do  you  see  the  small  pieces  of  amber  moving  about 
in  the  liquid  contained  in  this  phial? 
Caroline.  Yes,  perfectly. 

Mrs  B.  We  will  now  immerse  the  phial  in  a  glass  of  hot  water,  and 
the  motion  of  the  liquid  will  be  shown  by  that  which  it  communicates  to  the 
amber(ll). 

Emily.  T  see  two  currents,  one  rising  along  the  sides  of  the  phial,  the 
Other  descending  in  the  centre;  but  I  do  not  understand  the  reason  of  this. 

Mrs  B.  The  hot  water  communicates  its  caloric,  through  the  medium 
of  the  phial,  to  the  particles  of  the  fluid  nearest  to  the  glass;  these  dilate 
and  ascend  laterally  to  the  surface,  whilst  the  less  heated  particles,  distant 
from  the  surface  of  the  phial,  in  descending,  form  the  central  current(12). 

Caroline.  This  is  indeed  a  very  clear  and  satisfactory  experiment;  but 
how  much  slower  the  currents  now  move  than  they  did  at  first. 

Mrs  B.  It  is  because  the  circulation  of  particles  has  nearly  produced  an 
equilibrium  of  temperature  between  the  liquid  in  the  glass  and  that  in  the 
phial. 

Caroline.  It  appears,  then,  that  we  are  to  consider  liquids  themselves  as 
non-conductors. 

Mrs  B.  By  no  means;  for  although  they  are  heated  principally  by  means 
of  the  mobility  of  their  particles,  it  has  been  shown  by  very  satisfactory  ex- 
periments, that  fluids,  although  the  worst  conductors  known,  do  absolutely 
admit  of  the  conveyance  of  heat,  from  particle  to  particle,  like  solid  bo- 
dies(13).  The  term  non-conductors  of  heat  cannot  therefore  be  properly- 
applied  to  any  body  in  nature;  whenever  you  see  it  used  you  must  therefore 
understand  that  it  is  employed  relatively,  and  not  absolutely (14). 

In  many  instances  when  we  wish  to 
diffuse  heat  equally,  and  rapidly,  we 
employ  fluids  for  the  purpose.  This 
might  lead  to  the  conclusion  that  they 
are  among  the  best  conductors,  were  not 
the  contrary  plainly  proved;  their  adap- 
tation to  this  purpose  resulting  from  the 
ready  mobility  of  their  particles,  as 
you  now  understand.  One  or  two  strik- 
ing experiments,  however,  showing  how 
slowly  they  conduct  heat,  will  still  be  of 
use,  as  they  will  impress  the  fact  upon 
your  minds  indelibly. 

I  have  nearly  filled  this  glass  tube 
with  cold  water,  and  by  a  weight  have 
confined  a  piece  of  ice  at  the  bottom  of 
it.  I  hold  the  tube  sloping  over  the 
flame  of  a  lamp,  so  as  to  heat  the  wa- 
ter in  the  upper  part;  this  will  be  soon  made  to  boil,  whilst  the  ice  will  re- 


11.  By  what  means  may  the  currents  be  rendered  visible? 

12.  From  what  cause  will  two  currents  be  produced? 

13.  Are  fluids  really  non-conductors? 

14.  How  is  the  term  non-conductors  to  be  understood? 


36  CONVERSATIONS  ON  CHEMISTRY. 

main  below  unthawed  for  a  considerable  length  of  time.  If  we  had  allowed 
the  ice  to  float  upon  the  surface,  and  applied  the  heat  below,  the  ice  would 
have  been  melted  before  the  water  would  have  become  sensibly  warm(15). 

Caroline.  Yes,  in  that  case  the  water  which  had  become  heated  below 
•would  have  ascended  to  the  surface,  when  it  would  have  been  cooled  again 
by  its  contact  with  the  ice. 

Mrs  JS.  This  experiment  is  sometimes  varied  by  putting  some  coloured 
water  at  the  bottom  of  the  tube,  instead  of  the  ice.  The  clear  water  above 
may  be  boiled  without  disturbing  the  coloured  part;  but  if  the  heat  be  ap- 
plied below,  the  coloured  portion  will  be  seen  to  rise  to  the  surface(lS). 

The  little  apparatus  which  I  am  now  about  to 
use  exhibits  the  same  fact  very  satisfactorily.  It 
consists  of  a  very  Sensible  air  thermometer,  ce- 
mented into  the  lower  end  of  a  glass,  funnel-shap- 
ed vessel,  so  that  when  the  vessel  is  nearly  filled 
with  water,  the  bulb  of  the  thermometer  will  be  a 
little  below  its  surface.  Upon  this  water  I  pour 
a  portion  of  ether,  which  will  float  upon  it,  and  is 
a  very  inflammable  liquid.  I  then  set  fire  to  the 
ether,  and  it  will  continue  to  burn  for  a  considera- 
ble time,  without  affecting  the  thermometer,  as  JBTl'iTlHfr 
you  may  ascertain  by  noticing  the  pointer,  which  «r*wrlF=^Bi=' 
shows  the  height  at  which  the  coloured  liquid 
stands  in  the  tube(17). 

Emily.  That  is  equally  extraordinary  and  sa- 
tisfactory, and  I  am  sure  I  shall  recollect  it  when- 
ever I  smell  ether. 

Mrs  B.  We  shall  frequently  have  to  recur  to 
the  slow  communication  of  caloric  by  the  conduct- 
ing power  of  bodies,  and  will  now  examine  the 
second  mode  by  which  heat  is  distributed,  which 
you  recollect  is  RADIATION". 

Caroline.  We  have  already  learned  that  heat 
passes  off  in  rays  in  conjunction  with  light,  both 
from  the  sun  and  from  burning  bodies;  but  is  it 
not  likely  that  in  these  instances  the  light  is  the 
active  agent,  and  carries  the  heat  with  it  in  con- 
sequence of  the  two  being  combined  together. 

Mrs  B.  By  no  means:  in  their  property  of  passing  off  in  rays  which 
move  with  immense  velocity,  heat  and  light  appear  to  be  analogous.  But 
for  this,  the  calorific  rays  which  were  found  beyond  the  confines  of  those  of 


light  in  the  experiments  of  Herschel,  could  not  have  existed  there.     You 


also  know  that  if  a  piece  of  iron,  or  any  other  "body,  be  heated,  though  not 
sufficiently  so  to  emit  light  even  in  the  dark,  you  will  very  sensibly  feel  the 
heat  emanating  from  it  as  you  approach  it;  and  this,  of  course,  is  in  conse- 
quence of  radiation(lS). 

Emily.  May  not  the  heat  be  conducted  to  us  by  the  atmosphere  with 
which  it  is  surrounded,  and  the  radiation  be  in  this  case  merely  apparent. 

Mrs  B.  Were  you  placed  above  the  heated  body  this  might  be  the  case, 
as  the  air  which  is  heated  by  contact  with  the  body,  having  its  specific  gra- 
vity decreased,  immediately  ascends;  but  as  you  feel  the  heat  both  laterally 


15.  By  what  experiment  may  it  be  shown  that  fluids  are  bad  conductors? 

16.  How  may  this  experiment  be  varied? 

17.  How  may  the  fact  be  proved  by  burning  ether? 

18.  What  circumstances  prove  the  radiation  of  heat  alone 


FREE  CALORIC— RADIATION.  37 

and  downwards,  it  must  pass  by  radiation  alone.  The  experiments  which 
you  will  witness  on  this  subject  will  establish  the  fact  beyond  the  possibility 
of  a  doubt.  The  cooling  of  a  body  is  greatly  accelerated  by  the  presence 
of  air;  but  a  heated  body,  though  suspended  in  vacuo,  will  have  its  tempera- 
ture reduced  to  that  of  surrounding  bodies,  and  this  must  be  effected  by 
the  operation  of  radiation  alone(19). 

Caroline.  What  a  constant  bustle  there  must  be  among  the  particles  of 
caloric,  if  they  are  thus  perpetually  flying  aboutTrom  one  body  to  another; 
but  I  do  not  see  Avhy  this  should  always  be  the  case.  If  all  the  bodies  in  a 
room  are  of  the  same  temperature,  I  do  not  perceive  any  effect  that  is  to  be 
produced  by  radiation,  and  indeed  I  should  suppose  that  in  that  case  it 
does  not  take  place;  and  yetl  do  not  know  how  a  body  on  one  side  of  a  room 
should  know  that  there  is  a  cooler  body  on  the  opposite  side,  and  conse- 
quently begin  to  radiate(20). 

Mrs  B.  You  have  unconsciously  touched  a  theoretical  question  which 
has  divided  philosophers.  Some  have  believed  that  bodies  radiate  in  propor- 
tion only  to  the  excess  of  caloric  which  they  contain  above  surrounding  bo- 
dies, and  that,  as  you  suggest,  if  all  were  of  one  temperature,  radiation  would 
cease,  in  consequence  of  the  equal  tendency  of  the  particles  of  caloric  to 
fly  off.  A  more  generally  received  opinion  however  is,  that  caloric,  being 
composed  of  particles  which  are  mutually  repulsive,  is  constantly  flying 
off  in  all  directions,  with  immense  velocity(21). 

Without  pretending  to  decide  the  controversy,  we  will,  for  the  sake  of 
illustration,  adopt  the  latter  opinion,  and  suppose  all  bodies,  whatever  their 
temperature,  to  be  constantly  radiating  caloric.  Those  that  are  of  the  same 
temperature  give  out  and  absorb  equal  quantities,  so  that  no  variation  of 
temperature  is  produced  in  them;  but  when  one  body  contains  more  free 
caloric  than  another,  the  exchange  is  always  in  favour  of  the  colder  body, 
until  an  equilibrium  is  effected(22). 

Caroline.  This  reciprocal  radiation  surprises  me  extremely.  I  at  first 
thought,  that  the  hotter  bodies  alone  emitted  rays  of  caloric,  which  were 
absorbed  by  the  colder;  and  it  still  seems  unnatural  that  a  hot  body  should 
receive  any  calorie  from  a  cold  one,  even  though  it  should  return  a  great 
quantity. 

Mrs  B.  It  may  at  first  appear  so,  but  it  is  no  more  extraordinary  than 
that  a  candle  should  send  forth  rays  of  light  to  the  sun,  which  you  know, 
must  necessarily  happen(23). 

Caroline.  Well,  Mrs  B.,  I  believe  that  I  must  give  up  the  point. 
But  I  wish  I  could  see  these  rays  of  caloric;  I  should  then  have  greater  faith 
in  them. 

Mrs  B.  You  must  give  some  credit  to  your  reason,  as  well  as  to  your 
senses,  or  faith  is  out  of  the  question.  Your  reason  will  tell  you,  that  if  you 
gain  more  heat  than  you  lose,  the  gain  being  absolute,  the  sensation  of 
warmth  must  be  felt.  It  is,  therefore,  only  when  you  are  parting  with  it  to 
a  body  of  a  lower  temperature,  that  you  can  experience  the  sensation  of 
cold,  because  you  then  sustain  an  absolute  loss  of  caloric. 

Emily.  And  in  this  case  we  cannot  be  sensible  of  the  small  quantity  of 
heat  we  receive  in  exchange  from  the  colder  body,  because  it  serves  only 
to  diminish  the  loss(24). 


19.  What  facts  prove  that  the  heat  is  not  conducted  by  the  atmosphere? 

20.  What' remarks  does  Caroline  make  respecting  radiation? 

21.  What  two  theories  have  been  maintained  respecting  radiation? 

22.  What  is  the  theory  adopted  in  these  conversations? 

23.  What  analogy  with  mutual  radiation  does  light  afford? 

24.  Why  do  we  not  always  feel  the  loss  of  heat  by  radiation? 

D 


CONVERSATIONS  ON  CHEMISTRY. 


Mrs  B.  Very  well,  indeed,  Emily.  Professor  Pictet,  of  Geneva,  had 
made  some  very  interesting  experiments,  which  prove  not  only  that  caloric 
radiates  from  all  bodies  whatever,  but  that  these  rays  may  be  reflected,  ac- 
cording to  the  laws  which  govern  in  tbe  radiation  of  light(25).  I  shall  re- 
peat these  experiments  before  you,  having  procured  mirrors  fit  for  the  pur- 
pose; they  are,  as  you  see,  concave,  and  made  of  tin  highly  polished.  Those 
which  I  use  are  a  foot  in  diameter,  and  their  curvature  is  a  radius  of  nine 
inches;  the  focus  of  parallel  rays  being,  therefore,  four  and  a  half  inches  dis- 
tant from  the  centre  of  each  mirror.  In  the  focus  of  one  mirror  I  place 

Mr  Pictefs  Apparatus  for  the  Reflection  of  Heat. 


[A.  and  B,  concave  mirrors,  fixed  on  stands.  C,  heated  bullet,  placed  in 
the  focus  of  the  mirror  A.  D,  thermometer,  with  its  bulb  placed  in  the 
focus  of  the  mirror  B.  The  dotted  lines  show  the  course  of  the  rays  of 
heat  diverging  from  the  heated  ball  C,  then  rendered  parallel  by  the  mir- 
ror A,  whence  they  are  reflected  to  the  mirror  B,  from  which  they  con- 
verge, and  fall  upon  the  thermometer  in  its  focus  D.] 

an  iron  bullet,  about  two  inches  in  diameter,  and  heated,  but  not  to  a  de- 
gree sufficient  to  render  it  luminous.  The  rays  of  heat  which  fall  on  it  are, 
agreeably  to  the  property  of  concave  mirrors,  reflected  in  a  parallel  direc- 
tion, so  as  to  fall  on  a  similar  mirror,  which,  you  see,  is  placed  opposite  to 
the  first,  and  at  the  distance  of  about  ten  feet:  this  second  mirror  causes  the 
rays  to  converge  to  its  focus,  in  which  1  place  the  bulb  of  this  very  sensible 
air  thermometer.  Now,  observe  in  what  manner  it  is  affected  by  the  calo- 
ric which  is  reflected  on  it  from  the  heated  bullet.  The  air  is  dilated  in 
the  bulb  which  we  placed  in  the  focus  of  the  mirror,  and  the  liquor  is,  you 
see,  considerably  depressed  in  the  tube(26). 

Emily.  But  would  not  the  same  effect  take  place,  if  the  rays  of  caloric 
from  the  heated  bullet  fell  directly  on  the  thermometer,  without  the  assist- 
ance of  the  mirrors? 

Mrs  JS.  The  effect  would  in  that  case  be  so  trifling,  at  the  distance  at 
•which  the  bullet  and  the  thermometer  are  from  each  other,  that  it  would  be 
almost  imperceptible.  The  mirrors,  you  know,  greatly  increase  the  effect, 
by  collecting  the  large  quantity  of  rays  which  falls  upon  their  surface  into  a 
focus.  Place  your  hand  in  the  focus  of  the  mirror,  and  you  will  find  it  to  be 
hotter  there  than  in  situations  much  nearer  to  the  bullet. 

Emily.  That  is  very  true;  it  appears  extremely  singular  to  feel  the  heat 
diminish  in  approaching  the  body  from  which  it  proceeds. 


25.  What  did  Pictet  of  Geneva  prove  respecting  the  radiation  of  heat? 

26.  Describe  the  apparatus  used  by  him  for  radiation. 


FREE  CALORIC— RADIATION.  39 

Caroline.  And  the  mirror  which,  by  converging  the  rays,  produces  so 
much  heat,  is  itself  quite  cold. 

Mrs  B.  The  whole  of  the  rays  that  are  dispersed  over  the  sin-face 
of  the  mirror  are  collected  by  it  into  the  focus;  and  if  you  consider  how 
large  a  surface  the  mirror  presents  to  the  rays,  and,  consequently,  how 
much  they  are  diffused  in  comparison  with  what  they  are  at  the  focus,  which 
is  little  more  than  a  point,  I  think  you  can  no  longer  wonder  that  the  focus 
should  be  stf  much  hotter  than  the  mirror(27). 

The  mirrors  are  so  used  in  this  experiment  as  to  prove  that  the  calorific 
emanation  is  reflected  in  the  same  manner  as  light(28). 

Caroline.     And  the  result,  I  think,  is  very  conclusive. 

Mrs  B.  The  experiment  may  be  repeated  by  substituting  a  wax  taper  for 
the  bullet,  with  a  view  of  separating  the  light  from  the  caloric.  For  this 
purpose  a  transparent  plate  of  glass  must  be  interposed  between  the  mir- 
rors; for  light,  you  know,  passes  with  great  facility  through  glass,  whilst 
the  transmission  of  artificial  heat  is  almost  wholly  intercepted  by  it.  We  shall 
find,  however,  in  this  experiment,  that  some  few  of  the  calorific  rays  pass 
through  the  glass  together  with  the  light,  as  the  thermometer  indicates; 
but,  as  soon  as  the  glass  is  removed,  and  a  free  passage  left  to  the  caloric, 
it  will  manifest  a  considerably  higher  temperature(29). 

Emily.  That  light  and  heat  may  be  separated  is  equally  well  proved  by 
this  experiment  as  by  that  of  Dr  Herschel;  for  in  the  latter,  the  separation 
was  not  perfect,  any  more  than  in  that  of  Mr  Pictet. 

Caroline.  I  should  like  to  repeat  this  experiment,  with  the  difference 
of  substituting  a  cold  body  instead  of  a  hot  one,  to  see  whether  cold  would 
not  be  reflected  as  well  as  heat. 

Mrs  B.  That  experiment  was  proposed  to  Mr  Pictet  by  an  incredulous 
philosopher  like  yourself,  and  he  immediately  tried  it  by  substituting  a  piece 
of  ice  in  the  place  of  a  heated  bullet. 

Caroline.     Well,  Mrs  B.,  and  what  was  the  result? 

Mrs  B.     That  we  shall  see;  I  have  procured  some  ice  for  the  purpose. 

Emily.  The  thermometer  indicates  a  considerable  reduction  of  tempera- 
ture(30)! 

Caroline.  And  does  not  that  prove  that  cold  is  not  merely  a  negative 
quality,  implying  simply  an  inferior  degree  of  heat?  The  cold  must  be 
positive,  since  it  is  capable  of  being  reflected. 

Mrs  B.  So  it  at  first  appeared  to  Mr  Pictet;  but  upon  a  little  conside- 
ration he  found  that  it  afforded  only  an  additional  proof  of  the  reflection  of 
heat.  This  I  shall  endeavour  to  explain  to  you. 

According  to  our  theory,  we  suppose  that  all  bodies  whatever  radiate 
caloric:  the  thermometer  used  in  these  experiments,  therefore,  emits  rays 
of  heat  in  the  same  manner  as  any  other  substance.  When  its  temperature 
is  in  equilibrium  with  that  of  the  surrounding  bodies,  it  receives  as  much 
caloric  as  it  parts  with,  and  no  change  of  temperature  is  produced.  But 
when  we  introduce  a  body  of  a  lower  temperature,  such  as  a  piece  of  ice, 
which  parts  with  less  caloric  than  it  receives,  the  consequence  is,  that  its 
temperature  is  raised,  whilst  that  of  the  surrounding  bodies  is  proportion- 
ally lowered(3l). 

Emily.  If,  for  instance,  I  was  to  bring  a  large  piece  of  ice  into  this  room, 
it  would  in  time  be  melted,  by  absorbing  caloric  from  the  general  radiation 


27.   In  what  way  do  the  mirrors  increase  the  effect? 

•28.   What  is  the  principal  fact  proved  by  the  mirrors? 

29.   What  is  remarked  respecting  the  using  a  taper? 

SO.  What  would  be  the  effect  of  substituting  ice  for  the  heated  ball? 

3i.  How  is  this  explained? 


40  CONVERSATIONS  ON  CHEMISTRY. 

•which  is  going  on  throughout  the  room;  and  as  it  would  contribute  rery 
little  caloric  in  return  for  what  it  absorbed,  the  room  would  necessarily  be 
cooled  by  it. 

Mrs  B.  Just  so;  and  as  in  consequence  of  the  employment  of  the  mir- 
rors, a  more  considerable  exchange  of  rays  takes  place  between  the  ice  and 
the  thermometer,  than  between  these  and  any  of  the  surrounding  bodies, 
the  temperature  of  the  thermometer  must,  therefore,  be  lowered  more  than 
that  of  any  other  adjacent  object(32). 

Caroline.     I  confess  I  do  not  perfectly  understand  your  explanation. 

Mrs  JB.  This  experiment  is  exactly  similar  to  that  made  with  the  heated 
bullet:  for,  if  we  consider  the  thermometer  to  be  the  hot  body  and  the  ice 
to  be  the  thermometer,  the  difficulty  will  cease;  and  let  me  tell  you  that  ice 
has  actually  been  used  to  ascertain  the  quantity  of  heat  given  out  by  warmer 
bodies,  as  the  quantity  of  it  which  is  melted  will  be  proportioned  to  the 
heat  which  passes  into  it.  In  the  present  instance  if  the  quantity  of  heat 
radiated  by  the  bulb  be  represented  by  the  number  20,  and  that  from  the  ice 
by  the  number  10,  it  is  evident  that  the  former  mustlose  twice  as  much  as  it 
receives,  and  its  temperature  must  be  reduced,  without  its  being  necessary 
to  suppose  that  cold  passes  into  it(S3). 

There  is  another  view  which  may  be  taken  of  this  fact,  which  may  serve 
to  explain  it  more  familiarly.  The  effect  of  radiation  is  the  same  as  that 
of  slow  communication  by  contact.  Now  suppose  you  were  to  place  the 
bulb  of  the  thermometer  and  the  ice  in  contact  with  each  other,  what  would 
be  the  result? 

Emily.  Why,  to  be  sure,  the  thermometer  would  be  reduced  in  tempera- 
ture, as  it  must  part  with  a  portion  of  its  heat  to  the  colder  body. 

Mrs  JB.  And  this  must  as  truly  be  the  case  when  radiation  is  employed 
to  equalize  their  temperature,  the  operation  being  merely  facilitated  by  the 
employment  of  the  mirrors(34). 

Caroline.  You  have  explained  this  in  so  satisfactory  a  manner,  that  I 
must  confess  I  cannot  help  being  convinced  that  cold  has  no  real  claim  to 
the  rank  of  a  positive  being. 

Mrs  B.  Before  I  conclude  the  subject  of  radiation,  I  must  observe  to 
you,  that  different  bodies  (or  rather  surfaces)  possess  the  power  of  radiating 
caloric  in  very  different  degrees(35). 

Some  curious  experiments  have  been  made  by  Mr  Leslie  on  this  subject. 
He  ascertained  that  black  surfaces  radiate  more,  and  polished  metallic  sur- 
faces less  than  any  others;  the  degree  of  radiation  being  proportioned  to 
the  greater  or  less  brilliancy  of  the  metallic  surface(36). 

Emily.  Supposing  these  surfaces,  of  course,  to  be  all  of  the  same  tem- 
perature ? 

Mrs  B.  Undoubtedly.  I  will  now  show  you  the  very  ingenious  appa- 
ratus, by  means  of  which  he  made  these  experiments.  This  cubical  tin 
vessel,  or  canister,  has  each  of  its  sides,  externally,  different;  one  is  simply 
blackened  over,  the  next  very  much  tarnished  by  rubbing  quicksilver  upon 
it;  the  next  scratched  all  over  with  sand  paper,  and  the  fourth  highly 
polished. 

This  vessel,  which  is  a  cube  of  four  inches,  we  shall  fill  with  hot  water, 
so  that  there  can  be  no  doubt  that  all  its  sides  will  be  of  the  same  tempera- 


82.  In  what  way  do  the  mirrors  influence  the  result? 

83.  What  is  remarked  respecting  the  ice  being  considered  as  the  ther-» 
mometer? 

34.  How  is  the  fact  explained  by  analogy? 

35.  What  is  said  of  the  radiating  power  of  difforent  surfaces? 
86.  What  gradation  was  observed  in  their  radiation^ 


FREE  CALORICS-RADIATION.  41 

ture.  Now  let  us  place  it  in  the  focus  of  one  of  the  mirrors,  turning  each 
of  its  sides  towards  it  in  succession.  We  shall  begin  with  the  black  sur- 
face(37). 

Caroline.  It  makes  the  thermometer  which  is  in  the  focus  of  the  other 
mirror  show  a  considerably  increased  temperature.  Let  us  turn  the 
tarnished  surface  towards  the  mirror.  The  thermometer  now  falls  a  little: 
it  follows,  therefore,  that  this  side  does  not  emit  or  radiate  so  much  caloric 
as  the  blackened  side. 

.Emily.  This  is  very  surprising;  for  the  sides  are  exactly  of  the  same 
size,  and  must  be  of  the  same  temperature.  But  let  us  try  the  scratched 
surface. 

Mrs  JB.  The  thermometer  indicates  less  heat;  and  with  the  polished 
surface  still  less.  These  two  surfaces  therefore  radiate  less  and  less. 

Caroline.     I  think  I  have  found  out  the  reason  of  this. 

Mrs  JB.  I  should  be  very  happy  to  hear  it;  for  it  has  not  yet  (to  my 
knowledge)  been  accounted  for. 

Caroline.  The  water  within  the  vessel  gradually  cools,  and  the  thermo- 
meter shows  this. 

Mrs  B.  It  is  true  that  the  water  cools,  but  certainly  to  a  much  less 
extent  than  the  thermometer  indicates,  as  you  will  perceive  if  you  now 
change  the  bright  surface  for  the  black  one. 

Caroline.  I  was  evidently  mistaken;  for  the  thermometer  again  shows 
an  increase  of  heat,  now  that  the  black  surface  fronts  the  mirror. 

J\frs  JB.     And  yet  the  water  in  the  vessel  is  still  cooling,  Caroline. 

Emily.  I  am  surprised  that  the  bright  surface  should  radiate  the  least  calo- 
ric; for  a  metallic  vessel  filled  with  hot  water,  a  silver  tea-pot  for  instance, 
feels  much  hotter  to  the  hand  than  one  of  black  earthenware. 

Mrs  JB.  That  has  nothing  to  do  with  radiation,  but  is  owing  to  the  dif- 
ferent power  which  various  bodies  possess  for  conducting  caloric,  a  pro- 
perty which  we  have  already  examined(38).  Although  a  metallic  vessel 
feels  warm  to  the  hand,  a  polished  vessel  of  this  kind  is  known  to  preserve 
the  heat  of  the  liquid  within,  better  than  one  of  any  other  material;  as  it 
loses  but  little  by  radiation.  It  is  for  this  reason  that  silver  tea-pots  make 
better  tea  than  those  of  earthenware(39). 

It  has  also  been  found  that  colour  has  a  great  influence  upon  radiation. 
Thus  dark  coloured  cloths  radiate  more  heat  than  those  of  a  light  colour, 
although  they  are  alike  in  texture  and  material(40). 

Emily.  According  to  these  experiments,  white,  or  light-coloured  dresses, 
in  cold  weather,  should  keep,  us  warmer  than  black  clothes,  since  the  latter 
radiate  so  much  more  than  the  former. 

Mrs  JB.  And  that  is  actually  the  case  when  we  are  in  the  shade;  but  in. 
the  sunshine,  for  a  reason  which  you  will  presently  learn,  black  would  be 
the  warmest(4l). 

Emily.  This  property,  of  different  surfaces  to  radiate  in  different  de- 
grees, appears  to  me  to  be  at  variance  with  the  equilibrium  of  caloric;  since 
it  would  imply  that  those  bodies  which  radiate  most,  must  ultimately  be- 
come coldest.  Suppose,  for  example,  that  we  were  to  vary  the  experiment, 
by  using  two  metallic  vessels  full  of  boiling  water,  the  one  blackened,  the 
other  not;  would  not  the  black  one  cool  the  first? 


37.  What  kind  of  vessel  may  be  used  in  these  experiments? 

38.  Why  does  a  metallic  vessel  feel  hotter  than  one  of  earthenware  ? 

39.  Why  is  belter  tea  made  in  silver  than  in  earthen  tea-pots? 

40.  What  influence  has  colour  on  the  radiation  of  a  body? 

41.  What  effect  would  this  have  upon  dress? 

D  2 


42  CONVERSATIONS  ON  CHEMISTRY. 

Caroline.  True;  but  when  they  were  both  brought  down  to  the  tempe- 
rature of  the  room,  the  interchange  of  caloric  between  the  canisters  and  the 
other  bodies  in  the  room  being  then  equal,  their  temperatures  would  re- 
main the  same(42). 

Emily.  I  do  not  see  why  that  should  be  the  case;  for  if  different  surfaces 
of  the  same  temperature  radiate  in  different  degrees  when  heated,  why 
should  they  not  continue  to  do  so  when  cooled  down  to  the  temperature  of 
the  room? 

Mrs  B.  You  have  started  a  difficulty,  Emily,  which  certainly  requires 
explanation.  It  is  found  by  experiment,  that  the  power  of  absorption  cor- 
responds with,  and  is  proportional  to,  that  of  radiation;  or,  in  other  words, 
those  surfaces  which  part  with  heat  the  most  rapidly  by  radiation,  absorb 
radiant  heat  the  most  readily  from  other  bodies(43).  If  you  place  before 
the  fire  a  brigkt  tin  pot,  and  another,  the  surface  of  which  is  quite  black, 
the  black  surface  absorbs  heat  so  readily,  and  the  bright  one  so  slowly,  that 
water  contained  in  the  former  will  be  heated,  whilst  that  in  the  latter  will 
be  scarcely  warmed(44).  If  the  blackened  surface  therefore  radiates  heat 
with  eight  times  the  facility  of  a  polished  one,  it  also  absorbs  in  a  propor- 
tionate quantity  the  rays  which  fall  upon  it  from  other  bodies. 

It  was  to  this  facility  of  absorption  that  I  alluded  when  I  told  you  that  in 
the  sunshine,  a  black  dress  would  be  warmer  than  a  white  one,  as  it  would 
take  in  more  heat  by  absorption  than  it  would  lose  by  radiation.  In  winter, 
therefore,  it  would  be  preferable(45). 

You  now  understand  the  reason  why  polished  brass  andirons  remain  cool 
for  hours  before  a  large  fire,  whilst  those  which  are  unpolished  rapidly  be- 
come heated;  the  latter  absorbing,  and  the  former  reflecting  back  again, 
nearly  all  the  heat  which  falls  upon  them(46). 

Emily.  I  now  understand  this  extremely  well.  But  what  becomes  of 
the  surplus  of  calorific  rays,  which  good  radiators  emit,  and  bad  radiators 
refuse  to  receive?  they  must  wander  about  in  search  of  a  resting-place! 

Mrs  B.  They  really  do  so;  for  they  are  rejected  and  sent  back,  or,  in 
other  words,  reflected^  the  bodies  which  are  bad  radiators  of  caloric;  and 
they  are  thus  transmitted  to  other  bodies  which  happen  to  lie  in  their  way, 
by  which  they  are  either  absorbed  or  again  reflected,  according  as  the  pro- 
perty of  reflection,  or  that  of  absorption,  predominates  in  these  bodies(47). 

Caroline.  I  do  not  well  understand  the  difference  between  radiating  and 
reflecting  caloric;  for  the  caloric  that  is  reflected  from  a  body  proceeds 
from  it  in  straight  lines,  and  may  surely  be  said  to  radiate  from  it? 

Mrs  B.  It  is  true  that  there,  at  first,  appears  to  be  considerable  analogy 
between  radiation  and  reflection,  as  they  equally  convey  the  idea  of  the  trans- 
mission of  caloric  in  rays. 

If  you  consider  a  little,  you  will  soon  perceive  that  when  a  body  radiates 
caloric,  the  heat  which  it  emits  not  only  proceeds  from,  but  has  its  origin  in 
the  body  itself.  Whilst  when  a  body  reflects  caloric,  it  parts  with  none  of 
its  own  caloric,  but  only  sends  back  that  which  falls  upon  it  from  other 


Emily.     Of  this  difference  we  have  very  striking  examples  before  us,  in 


42.  What  is  remarked  respecting  two  vessels  differing  only  in  colour? 

43.  What  is  said  of  absorption? 

44.  What  would  be  the  difference  in  heating  water  in  a  bright  and  black- 
ened tin  pot,  and  why  ? 

45.  How  does  this  explain  a  former  remark  respecting  dress? 

46.  Why  do  polished  andirons  remain  cool  before  a  fire? 

47.  What  becomes  of  the  reflected  rays  of  heat? 

48.  What  is  the  difference  between  radiation  and  reflection? 


EFFECTS  OF  CALORIC— EXPANSION.  43 

i 

the  tin  vessel  of  water,  and  the  concave  mirrors;  the  first  radiates  its  own 
heat,  the  latter  reflect  the  heat  which  they  receive  from  other  bodies(49). 

•Mrs  B.  We  have  yet  much  to  say  upon  the  subject  of  free  caloric,  as 
we  have  hitherto  attended  only  to  its  nature,  and  the  manner  in  which  it  is 
distributed  among  bodies.  The  effects  which  it  produces  upon  them  will 
afford  ample  matter  for  another  conversation;  as  the  notice  of  these  effects 
will  lead  to  the  consideration  of  a  number  of  collateral  points  which  it  is 
important  you  should  understand. 


CONVERSATION  IV. 

ON  THE  EFFECTS  OF  CALORIC. 

Dilatation  of  Bodies.  Pyrometer.  Thermometer.  Fixed  Points.  Mr 
Thermometer.  Differential  Thermometer.  Exceptions  to  the  Law  of  Ex- 
pansion. Fusion  or  Liquefaction. 

Caroline.  I  had  no  idea  whatever  that  the  subject  of  heat  would  oc- 
cupy one  half  of  the  space  already  passed;  but  it  now  seems  to  me  that 
the  part  unexplored  by  us  is  more  extensive  than  that  over  which  we  have 
travelled,  as  we  have  yet  to  consider  the  effects  which  heat  produces  upon 
bodies,  and  these  must  certainly  be  numerous. 

J\frs  B.  A  knowledge  of  all  the  causes  and  effects  of  a  change  of  tem- 
perature in  bodies,  would  be  a  complete  knowledge  of  chemistry;  as  every 
change  in  the  nature  or  the  composition  of  any  substance  is  produced  or 
accompanied  by  a  variation  of  its  temperature(l).  You  will,  therefore,  at 
once  see  the  importance  of  giving  particular  attention  to  the  effects  produced 
upon  a  body  by  the  entrance  of  caloric  into  it.  These  effects  are,  1st, 
Expansion  or  Dilatation;  2d,  Fusion  or  Liquefaction;  3d,  Evaporation; 
and  4th,  Ignition  or  Incandescense(2). 

One  of  the  most  remarkable  properties  of  free  caloric  is  its  power  of 
expanding-  or  dilating-  bodies.  This  fluid  is  so  extremely  subtile,  that  it 
enters  and  pervades  all  bodies  whatever,  forces  itself  between  their  particles, 
and  not  only  separates  them,  but  frequently  drives  them  to  a  considera- 
ble distance  from  each  other.  It  is  thus  that  caloric  dilates  or  expands 
a  body  so  as  to  make  it  occupy  a  greater  space  than  it  did  before(3). 

Emily.  The  effect  it  has  on  bodies,  therefore,  is  directly  contrary  to 
that  of  the  attraction  of  cohesion  or  aggregation;  the  one  draws  the  particle? 
together,  the  other  drives  them  asunder. 

Jiffs  B.  Precisely.  There  is  a  continual  struggle  between  the  attrac- 
tion of  aggregation,  and  the  expansive  power  of  caloric(4);  and  from  the  ac- 
tion of  these  two  opposite  forces  results  those  various  forms  of  matter,  in  one 
of  which  all  ponderable  bodies  are  presented  to  us,  viz.  the  solid,  the 
liquid,  and  the  aeriform  or  gaseous.  Accordingly  we  find  that  most  sub- 
stances are  capable  of  passing  from  one  to  another  of  these  forms,  merely  in 
consequence  of  their  receiving  different  quantities  of  caloric(S). 


49.  What  may  serve  as  examples? 

1.  Why  is  the  subject  of  heat  of  special  importance? 

2.  In  what  order  are  its  effects  treated? 

3.  How  is  caloric  supposed  to  operate  in  dilating  bodies? 

4.  What  power  is  opposed  to  calorific  repulsion? 

5.  la  how  many  forms  are  bodies  presented  to  us? 


44  CONVERSATIONS  ON  CHEMISTRY. 

Caroline.  That  is  very  curious;  but  I  thjnk  I  understand  the  reason  of 
it.  If  a  great  quantity  of  caloric  is  added  to  a  solid  body,  it  introduces 
itself  between  the  particles  in  such  a  manner  as  to  overcome  the  attraction 
of  cohesion  in  so  great  a  degree,  that  the  body,  from  a  solid,  is  converted 
into  a  liquid(6). 

Mrs  B.  This  is  the  case  whenever  a  body  is  fused  or  melted;  but  when 
you  add  caloric  to  a  liquid,  can  you  tell  me  what  is  the  consequence? 

Caroline.  The  caloric  forces  itself  in  greater  abundance  between  the 
particles  of  the  fluid,  and  drives  them  to  such  a  distance  from  each  other, 
that  their  attraction  of  aggregation  is  wholly  destroyed,  and  the  liquid  is 
transformed  into  vapour(7). 

Mrs  B.  Very  well;  and  this  is  precisely  the  case  with  boiling  water, 
when  it  is  converted  into  steam  or  vapour,  and  with  all  bodies  that  .assume 
an  aeriform  state. 

Emily.     I  do  not  well  understand  the  word  aeriform. 
Mrs  B.     Any  elastic  fluid  whatever,  whether  it  be  merely  a  vapour,  or 
permanent  gas,  is  called  aeriform.    Steam  and  the  air  of  the  atmosphere  may 
serve  as  examples(S). 

Emily.  Are  bodies  in  all  these  forms  expanded  by  heat,  or  is  it  only 
•when  they  are  changed  from  one  to  the  other  that  this  dilatation  takes  place. 

Mrs  B.  It  is  a  general  law  that  bodies,  in  all  their  forms, 
are  expanded  by  heat,  and  contracted  by  coW(9).  That  this 
law  operates  on  solid  substances,  1  will  show  you  by  a  simple 
but  very  decisive  experiment.  I  have  here  a  brass  ball 
turned  perfectly  spherical,  and  a  ring  through  which,  as  you  j 
see,  it  will  just  pass,  when  both  are  at  the  same  temperature. 
I  now  dip  the  ball  into  boiling  water,  and  it  will  no  longer 
pass  through  the  ring,  but  on  heating  the  latter  in  the  same 
way  it  passes  as  before.  I  again  dip  the  ring  into  cold  water, 
and  it  becomes  too  small  to  admit  the  ball  through  it. 

Caroline.  I  knew  that  heat  expanded  bodies,  but  I  had 
no  idea  that,  with  so  small  a  degree  of  it,  this  effect  could 
be  rendered  so  very  conspicuous(lO). 

Mrs  B.  By  means  of  this  other  instrument  (called  a  py- 
rometer) we  may  estimate,  in  the  most  exact  manner,  the  dila- 
tations of  various  solid  substances  by  heat.  The  body  we  are 
how  going  to  submit  to  trial  is  this  small  iron  bar:  I  fix  it  to  the  apparatus, 
and  then  heat  it  by  lighting  the  lamps  beneath  a  metallic  box  through  which 
it  passes,  and  in  which  there  is  a  portion  of  water.  The  fluid  is  made  to 
boil,  and  heats  the  iron  bar.  When  the  bar  expands,  it  increases  in  length 
as  well  as  thickness,  and,  as  one  end  communicates  with  these  moveable 
levers,  whilst  the  other  end  is  fixed  and  immoveable,  no  sooner  does  it 
begin  to  dilate  than  it  presses  against  the  levers,  and  sets  in  motion  the  in- 
dex, which  points  out  the  degrees  of  dilatation  on  the  graduated  segment(ll). 


6.  How  does  heat  operate  in  converting  a  solid  into  a  liquid? 

7.  How  in  producing  the  aeriform  state? 

8.  What  is  meant  by  aeriform  ? 

9.  What  is  the  general  law  respecting  expansion? 

10.  How  may  the  expansion  of  solids  be  shown? 

11.  Describe  an  instrument  used  for  measuring  the  expansion  of  solids. 


EFFECTS  OF  CALORIC— EXPANSION. 

PrBOMETER. 


[The  box  a  contains  water  to  be  boiled,  ff'is  a  metal  rod  to  be  heated, 
which  passes  through  metallic  studs  g-  £•,  andthiswirea  is  fixed  firmly  at 
one  end,  and  at  the  other  presses  against  the  lever  6,  which  operates  on 
the  index  c,  causing  it  to  move  along  the  graduated  arc  d  to  the  distance 
of  an  inch,  whilst  the  barexpands  only  1-400  part  of  that  distance. 

The  box  a  may  be  removed,  and  the  lamps  placed  under  the  rod,  when, 
the  expansion  will  be  increased.] 

Emily.  This  is,  indeed,  a  very  curious  instrument;  but  I  do  not  under- 
stand the  use  of  the  levers.  Would  it  not  be  more  simple,  and  answer  the 
purpose  equally  well,  if  the  bar,  in  dilating,  pressed  directly  against  the  in- 
dex, and  put  it  in  motion  without  the  intervention  of  the  levers? 

Mrs  B.  The  use  of  the  levers  is  merely  to  multiply  the  motion,  and, 
therefore,  render  the  effect  of  the  caloric  more  obvious;  for  if  the  index 
moved  no  more  than  the  bar  increased  in  length,  its  motion  would  scarcely 
be  perceptible;  but  by  means  of  the  levers  it  moves  in  a  much  greater  pro- 
portion, which  therefore  renders  the  variations  far  more  conspicuous(12). 

By  submitting  different  bodies  to  the  test  of  the  pyrometer,  it  is  found 
that  they  are  far  from  dilating  in  the  same  proportion.  Different  metals 
expand  in  different  degrees,  and  other  kinds  of  solid  bodies  vary  still  more 
in  this  respect. 

Caroline.  I  suppose  that  this  difference  of  expansion  results  from  the 
different  force  with  which  the  particles  attract  each  other. 

J^frs  B.  You  are  perfectly  correct;  as  caloric  is  the  antagonist  of  cohe^ 
sion  or  aggregation,  it  would  necessarily  follow  that  those  bodies  which 
possess  the  greatest  tenacity  would  be  less  affected  by  a  given  quantity  of 
heat,  than  those  in  which  attraction  is  exerted  with  less  force(13). 

In  conformity  with  this  law,  we  shall  find  that  fluids  which  possess  but 
little  aggregation,  undergo  a  degree  of  expansion  far  exceeding  that  of  solid 
bodies(U). 

I  have  here  two  glass  tubes,  terminated  at  one  end  by  large  bulbs.  xWe 
shall  fill  the  bulbs,  the  one  with  spirit  of  wine,  the  other  with  water, 
I  have  coloured  both  liquids,  in  order  that  the  effect  may  be  more  conspicu- 
ous. The  spirit  of  wine,  you  see,  dilates  by  the  warmth  of  my  hand  as  I 
hold  the  bulb. 


12.  What  is  the  use  of  the  levers  in  this  instrument? 

13.  Why  do  different  solids  expand  differently? 

14.  How  does  this  law  affect  the  expansion  of  fluids? 


46  CONVERSATIONS  ON  CHEMISTRY. 

Emily.  It  certainly  does,  for  I  see  it  is  rising  into  the  tube.  But  water, 
it  seems,  is  not  so  easily  affected  by  heat;  for  scarcely  any  change  is  pro- 
duced on  it  by  the  warmth  of  the  hand. 

Mrs  B.  True:  we  shall  now  plunge  the  bulbs 
into  hot  water,  and  you  will  see  both  liquids  rise 
in  the  tubes;  but  the  spirit  of  wine  will  ascend 
highest. 

Caroline.  How  rapidly  it  expands!  Now  it 
has  nearly  reached  the  top  of  the  tube,  though  the 
water  has  hardly  begun  to  rise. 

Emily.  The  water  now  begins  to  dilate.  Are 
not  these  glass  tubes,  with  liquids  rising  within 
them,  very  like  thermometers(15)? 

Mrs  B.  A  thermometer  is  constructed  exactly 
on  the  same  principle,  and  is  in  fact  a  small  bottle 
with  a  long  narrow  neck.  Were  you  to  fill  such 
a  bottle  so  that  the  contained  fluid  reached  some 
way  up  the  neck,  you  would  find  it  rise  in  warm, 
and  subside  in  cold  weather,  as  in  these  tubes, 
which  require  only  a  scale  to  answer  the  purpose 
of  thermometers:  they  would,  however,  be  rather 
awkward  in  their  dimensions(lG).  The  tubes 
and  bulbs  of  thermometers,  though  of  various 
sizes,  are,  in  general,  much  smaller  than  these. 
The  tube  too  is  closed,  by  melting  the  end  of  it 

£  ~  tUUC,S  ami  uu.ua.  ^  ^  tQ  ^  the  logs    of  the  flu;d     ^  ^ 

B  B  vessels  of  warm  water.clude  ^  air      The  fluid  most  general,y  used  in 

thermometers,  is  mercury,  commonly  called  quicksilver,  the  dilatations  and 
contractions  of  which  correspond  more  exactly  to  the  additions  and  sub- 
tractions of  caloric,  than  those  of  any  other  fluid(17). 

Caroline.  Yet  I  have  often  seen  coloured  spirit  of  wine  used  in  ther- 
mometers. 

Mrs  B.  The  expansions  and  contractions  of  that  liquid  are  not  quite  so 
uniform  as  those  of  mercury;  nor  will  it  answer  for  temperatures  much 
above  the  heat  of  summer,  as  the  spirit,  if  more  highly  heated,  would  be 
converted  into  vapour.  There  are  two  cases,  however^  to  which  spirit  of 
wine  is  particularly  applicable:  from  its  great  expansibility  it  enables  us 
to  ascertain  very  slight  variations  of  temperature;  and  its  not  being  frozen 
by  the  most  intense  cold  with  which  we  are  acquainted,  renders  it  indispen- 
sable in  measuring  those  lower  degrees,  where  mercury  and  every  other 
known  fluid  is  converted  into  the  sol'-d  state(18). 

Emily.  I  have  often  seen  it  mentioned  that  the  heat  was  so  many  degrees 
of  Fahrenheit's  scale,  or  of  some  other  scale  that  was  named.  I  do  not  under- 
stand how  the  difference  of  the  scale  can  make  any  difference  in  the  heat  of 
the  weather,  or  in  that  of  any  other  thing. 

Mrs  B.  The  scale  of  a  thermometer  is  merely  a  flat  plate  placed  behind 
the  tube,  and  marked  with  small  divisions  to  show  to  what  height  the  fluid 
rises(19).  These  divisions,  like  the  weights  and  measures  of  different  coun- 
tries, are  arbitrary.  A  pound  or  a  foot  in  France  is  not  the  same  with  our 


A  A  tubes  and  bulbs. 


15.  By  what  experiment  is  the  different  expansion  of  liquids  shown? 

16.  In  what  respect    do    such  a  tube  and  bulb  resemble  a  thermometer? 

17.  What  fluid  is  generally  used  in  a  thermometer? 

18.  Spirit  of  wine  is  sometimes  used,  what  are  its  advantages  and  disad- 
vantages? 

19.  What  is  meant  by  the  scale  of  a  thermometer? 


EFFECTS  OF  CALORIC— EXPANSION.  47 

pound  or  foot;  so,  different  persons,  or  rather  different  countries,  have  adopt- 
ed scales  for  thermometers,  the  degrees  or  divisions  on  which  vary  much 
from  each  other(20).  All,  however,  proceed  upon  the  same  principle  in  ob- 
taining what  are  called  the  fixed  points.  These  fixed  points  are  the  tempe- 
rature at  which  water  freezes,  and  that  at  which  it  boils;  as,  under  ordinary 
circumstances,  these  effects  take  place  at  the  same  degree  every  where(21). 

In  making  a  mercurial  thermometer,  after  preparing  the  tube  with  a  bulb 
at  one  end,  the  bulb  and  a  part  of  the  tube  are  filled  with  quicksilver,  the 
quantity  put  in  being  such  that  it  will  stand  above  the  bulb  at  the  freezing, 
and  not  reach  the  top  of  the  tube  at  the  boiling  point.  It  is  then  seale.il 
hermetically,  dipped  into  freezing  water,  and  a  mark  made  on  the  tube  at  the 
point  to  which  the  mercury  sinks  when  in  this  situation:  it  is  afterwards 
placed  in  boiling  water,  and  a  similar  mark  made  at  the  point  to  which 
the  mercury  then  rises.  On  putting  it  into  boiling  or  freezing  water  at 
any  other  time,  it  will  rise  and  fall  to  the  same  points.  The  tube  thus 
prepared  is  fitted  on  a  piece  of  metal  or  ivory,  which  is  to  be  so  divided 
as  to  form  the  scale.  In  doing  this  the  boiling  and  freezing  points  are 
first  transferred  to  the  scale,  whatever  is  to  be  the  subsequent  division(22). 

Caroline.  Then  if  thermometers  were  wanted  to  show  these  two  points 
only,  they  would  be  alike  in  every  country. 

J\frs  B.  Yes,  and  it  is  the  number  of  parts  into  which  the  spaces  be- 
tween these  points  are  divided  which  constitutes  the  difference  in  the  degrees. 
There  afe  three  different  scales  which  you  ought  to  know,  as  they  are  each 
in  use,  and  two  of  them  extensively;  these  are  Reaumur's,  the  Centigrade, 
and  Fahrenheit's^}.  The  former  is  divided  into  eighty  parts  or  degrees, 
between  the  freezing  and  boiling  points,  so  that  by  it  water  freezes  at  0°  and 
boils  at  80°(24).  The  centigrade  is  now  generally  used  in  France,  and  is 
divided  between  the  two  fixed  points,  into  one  hundred  parts;  the  freezing 
point  is  0°  and  the  boiling  point  100°(25).  In  both  these  thermometers  you 
count  the  degrees  from  the  freezing  point,  the  degrees  below  being  called  so 
many  below  freezing,  or  the  term  minus  being  used(26). 

The  thermometer  used  in  this  country  and  in  England  is  Fahrenheit's. 
This  is  divided  into  180°  between  the  freezing  and  boiling  points,  and  32°  of 
the  same  size  are  then  laid  off  below  the  freezing  point.  From  the  last  degree 
so  laid  off  this  scale  begins;  so  that  the  freezing  point  is  called  32°,  and  the 
boiling  point  212°;  thirty-two  and  eighty  making  that  number(27). 

Emily.  The  variety  of  scales  must  be  very  inconvenient,  and,  I  should 
think,  liable  to  occasion  confusion  in  comparing  our  experiments  and  ob- 
servations with  those  of  the  continent  of  Europe. 

Mrs  B.  It  is  certainly  inconvenient,  as  it  gives  some  trouble,  but  need 
not  create  any  confusion;  it  being  easy  to  compare  one  scale  with  another, 
when  we  know  the  relative  length  of  their  divisions.  In  Reaumur's  each 
degree  is  equal  to  2£  of  Fahrenheit's;  and  five  degrees  of  the  centigrade 
are  equal  to  nine  of  Fahrenheit.  In  comparing  them,  however,  it  must  be 
recollected  that  the  scale  of  the  latter  commences  32°  below  freezing(28). 
The  thermometer  which  I  now  show  you  has  two  of  these  scales,  Fahren- 


20.  What  has  led  to  the  adoption  of  different  scales? 

21.  What  are  the  fixed  points  in  a  thermometer? 

22.  State  the  general  mode  of  procedure  in  making  a  thermometer. 

23.  What  are  the  three  scales  denominated  which  are  in  use? 

24.  In  what  way  is  the  scale  of  Reaumur  divided? 

25.  How  is  the  centigrade  divided,  and  where  is  it  used? 

26.  How  are  the  degrees  above  and  below  freezing  designated? 

27.  In  what  way  are  the  divisions  of  Fahrenheit  obtained? 

28.  In  what  way  are  these  three  scales  compared  ? 


48 


CONVERSATIONS  ON  CHEMISTRY. 


water 


212 
210 


190 


150 


belt's  and  the  centigrade,  one  on  each  side  of  the  tube.    (Seethe  word  ther- 
mometer in  the  glossary). 

Caroline.  The  centigrade  seems  to  me 
the  most  reasonable  division;  and  I  cannot 
imagine  why  the  freezing  point  is  called  32°, 
or  what  advantage  is  derived  from  it. 

Mrs  B.  There  really  is  no  advantage  in 
it;  and  it  originated  in  a  mistaken  opinion  of 
the  instrument-maker,  Fahrenheit,  who  first 
boils,  constructed  these  thermometers.  He  mixed 
snow  and  salt  together  and  produced  by  that 
means  a  degree  of  cold  which  he  concluded 
was  the  greatest  possible,  and  therefore  made 
his  scale  begin  from  that  point(29). 

Emily.  Are  spirit  of  wine  and  mercury 
the  only  liquids  used  in  the  construction  of 
thermometers? 

Mrs  B.  They  are  the  only  liquids  in  gen- 
eral use  for  this  purpose;  but  for  experi- 
ments in  which  a  very  quick  and  delicate  test 
of  the  changes  of  temperature  is  required,  air 
is  sometimes  employed(SO).  The 
bulb  of  an  air  thermometer  is  filled 
with  common  air  only,  and  the  tube 
or  stem,  which  should  be  sixteen  or 
eighteen  "inches  long,  has  its  end 
left  open.  If  this  end  be  inverted  in 
a  cup  containing  some  coloured 
liquid,  and  the  bulb  grasped  in  the 
warm  hand,  the  air  within  being 
expanded,  will  be  seen  bubbling  up 
through  the  liquid.  On  withdrawing 
the  hand,  the  air  will  contract  by 
cooling,  and  in  consequence  the  li- 
quid will  gradually  ascend  in  the 
tube,  its  altitude  always  depending 
on  the  expansion  and  contraction  of 
the  air.  The  amount  of  this  expan- 
sion and  contraction  may  be  indi- 
'cated  by  a  scale(31). 

Such  was  the  first  kind  of  thermo- 
meter made,  and  it  was  the  invention 
of  Sanetdrio,  an  Italian  philosopher. 
It  is  found  very  useful  for  detecting 
minute  changes  of  temperature  in 
many  chemical  experiments.  If  I 
merely  breathe  on  the  bulb  you 
will  see  that  the  liquid  sinks,  and  if 
I  then  blow  on  it  that  it  rises(32). 

Caroline.    This  instrument  serves 


water 


100 


90 


60 


freez.. 


29.  What  led  Fahrenheit  to  the  adoption  of  his  zero? 

30.  What  forms  the  most  delicate  thermometer? 

31.  Describe  the  construction  and  operation  of  the  air  thermometer. 

32.  What  is  said  in  proof  of  its  great  sensibility? 


EFFECTS  OF  CALORIC—EXPANSION. 


49 


Differential 
Thermometer.  \ 


also  to  show  the  expansion  of  air  by  heat,  and  that  in  this  respect  it  greatly 
exceeds  either  solids  or  liquids. 

Mrs  B.  You  have  anticipated  my  calling  yowr  attention  to  this  fact,  as 
it  completes  the  evidence  of  the  expansion  of  bodies  in  all  their  forms. 
That  the  dilatation  of  air  should  be  greater  than  that  of  solids  or  liquids 
follows  of  necessity,  from  the  circumstance  of  there  being  in  it  no  attraction 
of  cohesion  to  overcome(33). 

Before  dismissing  the  air  thermometer  I  w 
show  you  one  of  a  very  peculiar  construction, 
which  was  contrived  by  Mr  Leslie  to  use  in 
experiments  on  the  radiation  of  heat  from  differ- 
ent  surfaces.  It  is  called  the  differential  ther- 
mometer, and  consists  of  a  glass  tube  nearly  in  the 
form  of  the  letter  U,  with  a  bulb  at  each  termi- 
nation. Each  of  these  bulbs  contains  air,  and  there 
is  some  coloured  liquid  in  the  tube  which  moves 
when  the  air  in  only  one  of  the  bulbs  is  dilated 
or  contracted,  but  remains  stationary  whenever 
they  are  both  exposed  to  the  same  temperature. 
If,  therefore,  you  take  the  instrument  from  one 
room  to  another  of  a  different  temperature,  as  the 
air  in  each  bulb  will  be  equally  expanded  or  con- 
tracted, the  liquid  will  not  show  any  evidence  of 
the  cbange(34). 

Emily.  This  seems  rather  a  strange  kind  of 
thermometer  which  undergoes  no  change  in  be- 
ing removed  from  a  hot  into  a  cold  place. 

Mrs  B.  The  name  of  differential  was  given 
to  it,  because  it  shows  the  difference  of  tempera- 
ture in  the  two  bulbs.  It  was  on  this  account  pe- 
culiarly adapted  to  Mr  Leslie's  experiments, 
when  one  bulb  was  placed  in  the  focus  of  the  mirror;  for  it  would  remain 
unaffected  by  every  change  of  temperature  in  the  room,  but  indicate  any 
variation  which  took  place  in  the  focus  by  radiation(35). 

Emily.  But  do  common  thermometers  indicate  the  exact  quantity  of  ca- 
lorie contained  either  in  the  atmosphere,  or  in  any  body  with  which  they 
are  in  contact? 

Mrs  B.  No:  first,  because  there  are  modifications  of  caloric  which  do 
not  affect  the  thermometer;  it  is  in  fact  only  the  free  caloric  which  does 
affect  it;  and,  secondly,  because  the  temperature  of  a  body,  as  indicated  by 
the  thermometer,  is  only  relative.  When,  for  instance,  the  thermometer 
remains  stationary  at  the  freezing  point,  we  know  that  the  atmosphere,  (or 
medium  in  which  it  is  placed,  whatever  it  may  be],  is  as  cold  as  freezing 
water;  and  when  it  stands  at  the  boiling  point,  we  know  that  this  medium  is 
as  hot  as  boiling  water;  but  we  do  not  know  the  positive  quantity  of  heat 
contained  either  in  freezing  or  boiling  water,  any  more  than  we  know  the 
real  extremes  of  heat  and  cold;  and  consequently  we  cannot  determine  that 
of  the  body  in  which  the  thermometer  is  placed(36). 

Caroline.     I  do  not  quite  understand  this  explanation. 

Mrs  B.  Let  us  compare  a  thermometer  to  a  well,  in  which  the  water 
rises  to  different  heights,  according  as  it  is  more  -or  less  abundantly  supplied 


33.  What  reason  exists  that  air  should  dilate  more  than  other  bodies? 

34.  Describe  the  differential  thermometer. 

35.  Why  is  it  so  called,  and  to  what  particular  use  was  it  applied? 

36.  Does  a  thermometer  indicate  the  quantity  of  caloric  in  a  body? 

E 


50  CONVERSATIONS  ON  CHEMISTRY. 

by  the  spring  which  feeds  it.  If  the  depth  of  the  well  is  unfathomable,  it 
must  be  impossible  to  know  the  absolute  quantity  of  water  it  contains;  yet 
we  can  with  the  greatest  accuracy  measure  the  number  of  feet  the  water 
has  risen  or  fallen  in  the  well  at  any  time,  and  consequently  know  the  pre- 
cise quantity  of  its  increase  or  diminution,  without  having  the  least  know- 
ledge of  the  whole  quantity  of  water  it  contains(37). 

Caroline.  Now  I  comprehend  it  very  well:  nothing  appears  to  me  to  ex- 
plain a  thing  so  clearly  as  a  comparison. 

Emily.     But  will  thermometers  bear  any  degree  of  heat? 

Mrs  B.  No:  for  if  the  temperature  were  much  above  the  highest  degree 
marked  on  the  scale  of  the  thermometer,  the  mercury,  by  its  expansion,  would 
burst  the  tube:  and  no  thermometer  can,  on  any  account,  be  applied  to 
temperatures  higher  than  the  boiling  point  of  the  liquid  used  in  its  con- 
struction; for,  on  the  liquid  beginning  to  boil,  the  steam  would  burst  the 
tube(38). 

Caroline.  True,  this  point  must  limit  the  degree  of  heat  which  can  be 
measured  by  the  thermometer;  but  how  then  can  we  ascertain  the  high 
temperature  of  our  fires,  and  of  furnaces? 

Mrs  B.  There  is  yet  no  accurate  instrument  known  for  effecting  this, 
although  several  have  been  devised.  That  which  has  been  most  depended 
upon  is  a  pyrometer  invented  by  Wedgwood.  Clay  possesses  the  property  of 
contracting  in  the  fire  to  a  very  considerable  extent,  and  in  a  degree  which 
is  proportioned  to  the  heat  to  which  it  has  been  exposed(39).  To  take  ad- 
vantage of  this  property,  Mr  Wedgwood  used  a  particular  kind  of  clay, 
which  he  baked  so  as  to  expel  the  moisture  contained  in  it.  Pieces  of  this, 
half  an  inch  in  diameter,  were  placed  in  an  earthen-ware,  glass-house,  or 
other  furnace,  and  when  taken  out  they  were  measured  by  a  particular  kind 
of  gauge,  to  ascertain  how  much  they  had  diminished  in  bulk,  and  from  this 
diminution  the  degree  of  heat  was  estimated(40). 

Emily.  And  what  has  been  the  difficulty  in  the  use  of  this  means  for  the 
purpose  intended?  I  can  see  none,  if  the  clay  shrinks  in  proportion  to  the 
heat. 

Mrs  B.  Besides  some  other  objections,  it  has  been  found  that  the  clay 
will  decrease  in  bulk  by  a  lengthened  exposure  to  the  same  temperature, 
and  that  its  indications  were  nottherefore  to  be  depended  upon(4l).  The  ob- 
servations made  by  it,  however,  are  useful,  although  not  considered  as  per- 
fectly accurate. 

Caroline.  It  seems  that  in  this  case  we  have  to  unlearn  what  you  have 
just  been  taking  so  much  trouble  to  teach  us,  that  all  bodies  are  expanded 
by  heat;  for  you  tell  us  that  it  contracts  the  clay(42). 

Mrs  B.  There  is  certainly  much  difficulty  on  this  point,  arising  un- 
doubtedly from  the  imperfection  of  our  knowledge.  Whether  in  the  instance 
we  are  considering,  the  clay  affords  a  real,  or  only  an  apparent  exception  to 
a  very  general  law,  is  still  a  question.  When  it  is  first  put  into  the  fire  it 
is  a  porous,  spongy  mass;  when  it  comes  out,  it  is  close  and  compact.  Al- 
though it  has  not  undergone  fusion,  still  the  fire  has  had  the  effect  of  so  ar- 
ranging its  particles  as  to  diminish  the  quantity  of  pore,  and  consequently, 
to  lessen  the  dimensions  of  the  mass.  After  the  piece  has  been  taken  from 


37.  How  is  this  illustrated  by  comparison? 

38.  What  limits  the  temperature  measured? 

39.  What  particular  property  is  possessed  by  clay? 
40  In  what  way  did  Mr  Wedgwood  employ  it? 

41.  What  circumstance  rendered  it  Inaccurate? 

42.  What  does  the  contraction  of  the  clay  seem  to  contradict? 


EFFECTS  OF  CALORIC— EXPANSION.         51 

.  f.  "'.; 

the  fire,  however,  and  allowed  to  cool,  it  will  then  be  found,  like  other  bo- 
dies, to  expand  by  heat  and  contract  by  cold(43). 

Caroline.  If  there  are  no  other  exceptions  to  the  law  than  this,  I  shall 
feel  inclined  to  be  satisfied;  but  if  there  are  many  such,  I  scarcely  think  it 
ought  to  be  called  a  law. 

Mrs  B.  I  know  of  but  one  other,  which,  to  a  certain  extent,  is  a  real 
'exception,  and  one  which  we  shall  find  to  be  wisely  ordered,  for  a  most 
beneficent  purpose  in  the  economy  of  nature.  The  substance  in  which  it 
takes  place  is  water(44). 

Emily.  But  did  we  not  see  that  water  expanded  by  heat,  and  contracted 
by  cold,  as  well  as  spirit  of  wine,  although  in  a  less  degree? 

Mrs  B.  You  are  perfectly  correct:  as  water  is  cooled,  it  continues  to 
contract  until  it  arrives  at  40°,  which  you  know  is  8°  above  the  freezing 
point;  but  after  this  it  absolutely  expands  until  it  descends  to  32°,  when  it 
begins  to  freeze(45). 

Caroline.      I  should  like  to  know  the  cause  of  this. 

Mrs  B.  And  1  should  be  pleased  if  I  could  tell  it  to  you.  The  most 
plausible  explanation  of  it  that  I  have  met  with,  is  founded  on  the  known 
fact  that  water  when  it  freezes  expands  considerably;  ice  being  less  dense  than 
water.  That  arrangement  of  the  particles  upon  which  the  increased  bulk 
depends,  must  take  place  whilst  they  are  in  a  fluid  state,  and  this  it  has 
been  supposed  commences  at  40°  and  is  completed  at  32°(46). 

Although  the  cause  may  be  obscure,  the  beneficial  effect  of  the  circum- 
stance we  are  considering  is  evident.  This  property  of  water,  in  conjunc- 
tion with  its  previous  contraction,  prevents  the  freezing  of  deep  lakes,  even 
in  very  cold  climates,  and  causes  our  rivers  and  other  comparatively  shal- 
low waters  to  freeze  at  the  surface  only(47). 

Can  you  tell  me,  Emily,  what  will  be  the  effect  upon  a  body  of  water, 
when  the  atmosphere  becomes  so  cold  as  to  be  below  the  freezing  point? 

Emily.  I  think  so.  The  cold  air  will  deprive  the  "water  of  a  portion  of 
its  caloric  at  the  surface,  and  this  cooled  water  being  rendered  more  dense, 
will  descend,  and  expose  a  new  stratum  to  the  air;  and  unless  the  weather 
should  change,  this  process  will  continue  until  all  the  water  is  brought  to  the 
temperature  of  the  air. 

Mrs  B.  In  the  former  part  of  your  explanation,  you  are  right;  in  the 
latter,  wrong.  The  cooled  stratum  of  water  will  descend  until  the  whole  is 
reduced  to  40°;  but  after  this,  as  it  cools,  it  expands,  and  therefore  the  in- 
ternal motion,  occasioned  by  the  increased  specific  gravity  of  the  condensed 
particles,  ceases;  for  when  the  water  at  the  surface  no  longer  condenses,  it 
will  no  longer  descend,  and  leave  a  fresh  portion  exposed  to  the  atmosphere. 
The  same  surface,  therefore,  will  be  further  deprived  of  its  caloric,  and 
will  soon  be  brought  down  to  the  freezing  point.  When  it  becomes  ice, 
this  being  a  bad  conductor  of  heat,  preserves  the  water, beneath  a  long 
time  from  being  affected  by  the  external  cold(48). 

In  very  deep  lakes  the  whole  length  of  winter  is  insufficient  to  produce 
this  effect;  and  in  rivers,  and  all  other  waters,  when  the  surface  is  frozen, 
that  below  is  still  above  the  freezing  point,  and  may  be  at  40  degrees(49). 

Caroline.     And  the  sea  also  does  not  freeze,  1  suppose,  because  its  depth 


4S.  What  remarks  are  made  respecting  this  contraction? 

44.  What  other  body  furnishes  an  exception  to  the  law  of  expansion? 

45.  Under  what  circumstances  does  this  exception  exist? 

46.  To  what  cause  is  it  attributed? 

47.  What  benefit  results  from  it? 

48.  What  is  the  process  of  cooling  in  deep  water? 

49.  What  is  the  consequence  in  very  deep  lakes  and  iu  rivers' 


52  CONVERSATIONS  ON  CHEMISTRY. 

4 

is  so  great,  that  the  frost  never  lasts  long  enough  to  hring  down  the  tempe- 
rature of  such  a  vast  body  of  water  to  40  degrees? 

M'^s  B.  That  is  one  reason  why  the  sea,  as  a  large  mass  of  water,  does 
not  freeze.  But,  independently  of  this,  salt  water  does  not  freeze  till  it  is 
cooled  much  below  32  degrees.  Salt  water  is  also  an  exception  to  the  law 
of  condensation,  obeyed  by  fresh  water,  as  it  continues  to  condense  even 
many  degrees  below  the  freezing  point.  When  the  caloric  of  fresh  water, 
therefore,  is  imprisoned  by  the  ice  on  its  surface,  the  ocean-  still  continues 
throwing  off  heat  into  the  atmosphere,  which  is  a  most  signal  dispensation 
of  Providence  to  moderate  the  intensity  of  the  cold  in  winter(SO). 

This,  as  well  as  some  other  points  connected  with  changes  of  temperature 
in  several  of  the  operations  of  nature,  you  will  more  perfectly  understand 
after  having  attended  to  combined  caloric,  which  will  be  the  subject  of  our 
next  conversation.  Do  you  recollect  our  second  division  of  the  effects  of 
caloric? 

Emily.  Yes,  very  well;  it  was  fusion  or  liquefaction(51),  which  we 
know  takes  place  in  a  great  number  of  bodies;  but  I  think  we  shall  find 
more  exceptions  to  this  than  to  the  law  of  expansion. 

Mrs  B.  Perhaps  you  may  find  more  apparent,  but  no  real  exceptions. 
The  property  of  repulsion  is  manifestly  owing  to  caloric;  and  as  it  is  easy, 
within  certain  limits,  to  increase  or  diminish  the  quantity  of  this  principle 
in  any  substance,  it  follows  that  the  forms  of  bodies  may  be  made  to  vary  at 
pleasure;  that  is,  by  a  sufficiently  intense  heat  every  solid  may  be  converted 
into  a  fluid,  and  every  fluid  into  the  aeriform  staie(52).  This  inference  is 
so  far  justified  by  experience,  that  it  may  safely  be  considered  as  a  general 
law.  The  temperature  at  which  liquefaction  takes  place,  is  called  the  melt- 
ing tor  fusing  point;  and  that  at  which  liquids  become  solids,  the  point  of 
congelation(53).  For  each  individual  substance  these  points  are  the  same, 
&s  32°  is  the  point  of  fusion  and  of  congelation  for  water;  but  in  the  fusing 
point  of  different  substances,  as  of  ice  and  of  iron,  there  is  an  immense 
variation(54). 

Caroline.  It  seems  to  me  that  the  distinction  of  solid  and  fluid  is  alto- 
gether accidental,  as  it  depends  upon  the  temperature  to  which  a  body  is 
exposed. 

Mrs  B.  It  is  undoubtedly  so.  Were  the  medium  temperature  of  our 
globe  below  32°,  we  should  class  water  among  solids,  and  speak  of  its  fusion 
as  we  now  do  of  that  of  wax  or  tallow.  Abstracting  the  operation  of 
caloric,  therefore,  the  natural  state  of  all  bodies  would  be  the  solid(55). 

Emily.  All  then  that  is  necessary  to  convert  a  solid  into  a  fluid  is  to 
destroy  the  attraction  of  cohesion  among  its  particles. 

Mrs  B.  Not  exactly  so.  When  you  reduce  a  solid  to  an  impalpable 
powder  you  destroy  its  attraction  of  cohesion,  but  you  do  not  thereby  form  a 
fluid.  In  a  fluid  the  attraction  of  cohesion  is  not  destroyed,  but  only  modi- 
fied by  the  agency  of  taloric.  Drops  of  water  and  of  other  liquids  cohere; 
two  small  drops  of  water,  or  globules  of  mercury,  if  brought  into  contact, 
will  run  into  one,  manifesting  a  considerable  force  of  attraction(56). 

Caroline.  There  appears  to  me  much  difficulty  in  conceiving  how  a  body 
can  be  a  fluid  whilst  its  particles  attract  each  other,  as  it  is  upon  this  pro- 


50.  Does  salt  water  obey  the  same  law? 

51.  After  expansion,  what  is  the  next  general  effect  of  heat? 

52.  What  remarks  are  made  on  the  liquefaction  of  solids  ? 

53.  What  are  the  two  points  called  at  which  the  change  occurs? 

54.  What  is  said  respecting  the  fusing  point  of  different  bodies? 

55.  What  is  said  of  the  natural  state  of  bodies? 

56.  W7hat  respecting  attraction  in  fluids? 


EFFECTS  OF  CALORIC— LIQUEFACTION.  53 

perty  that  solidity  depends;  yet  it  is  evident  that  in  these  particles  attraction 
is  not  destroyed. 

J\frs  B.  Fluidity  has  heen  considered  as  depending  upon  the  equable 
attraction  of  the  particles  in  whatever  position  they  may  he  placed.  Solids 
are  supposed  to  be  such  because  the  particles  of  which  they  are  composed 
attract  each  other  with  greater  force  in  certain  directions  than  they  do  in 
others,  and  a  corresponding  power,  therefore,  will  be  necessary  to  alter 
their  positions;  but  if,  by  introducing  caloric,  you  can  equalize  the  attrac- 
tion so  that  it  remains  the  same  in  every  direction,  there  then  being  no  re- 
sistance from  attraction,  the  particles  will  move  among  themselves  with 
perfect  facility,  and  it  is  this  which  constitutes  fluidity(57). 

Caroline.  The  reasoning  appears  to  me  to  be  satisfactory,  and  yet  there 
is  a  something  in  the  action  of  these  particles  which  seem£  to  make  it  very 
difficult  to  reason  about  them;  for  although  they  must  exist,  it  is  not  as  sen- 
sible objects  that  they  do  so,  but  as  mere  ideas  of  the  mind. 

Emily.  I  have  been  looking  for  an  explanation  of  the  exceptions  to  this 
law,  which  seem  to  me  to  present  themselves  in  crowds.  Wood,  linen, 
paper,  coal,  and  many  other  things  undergo  combustion  without  showing 
the  least  tendency  to  fusion(58). 

Jlfrs  B.  Your  enumeration  of  apparent  exceptions  is  very  good,  and  it 
is  perfectly  natural  that  they  should  present  themselves  to  you  as  really 
such;  but  all  the  various  articles  of  which  these  bodies  are  composed,  are 
in  other  combinations,  frequently  found  in  the  fluid  state(59).  Such  sub- 
stances as  you  have  mentioned  do  not  become  fluid  when  subjected  to  the 
action  of  heat,  because  they  are  decomposed  at  a  temperature  below  that 
which  is  requisite  for  their  fusion.  In  proof  of  this,  chemists  have  effected 
the  fusion  of  some  of  them,  by  the  adoption  of  such  means  as  prevented  their 
decornposition(60). 

Carolijie.  There  appears  to  be  something  more  than  mere  decomposi- 
tion in  the  combustion  of  these  bodies.  They  not  only  escape  from  being 
converted  into  fluids,  but  actually  go  out  of  existence.  From  wood,  for 
example,  a  little  smoke  flies  off,  and  some  light  ashes  remain  behind,  but 
the  larger  part  of  it,  both  in  weight  and  bulk,  vanishes  entirely(Gl). 

Jlfrs  B.  You  will  soon  learn  that  not  an  atom  of  it  is  lost;  that  although 
the  chemical  union  is  dissolved,  the  matter  remains,  possessed  of  all  its  me- 
chanical attributes.  The  solid  substance  has  been  converted  by  heat  into 
invisible,  elastic  fluids,  but  in  this  there  is  no  approach  towards  annihilation. 
We  may  alter  the  forms  of  bodies,  but  we  have  no  more  power  to  destroy  a. 
single  particle  of  matter  than  we  have  to  create  it.  Whilst  reason  sanctions, 
chemistry  most  beautifully  exemplifies  the  universality  of  this  truth(62). 

Heat  not  only  liquefies,  but  may  be  rendered  sufficiently  intense  to  convert 
most  bodies  into  vapour,  and  we  believe  that  in  their  nature,  all  are  suscepti- 
hle  of  the  same  change,  although  we  have  not  yet,  in  every  instance,  succeed- 
ed in  effecting  it(63).  Evaporation,  you  know,  is  the  third  general  effect  of 
free  caloric.  This,  with  ignition,  we  will  tulk  about  to-morrow;  and  how- 
ever interesting  you  may  have  found  those  effects  of  heat  which  we  have 
already  examined,  that  which  we  have  next  to  consider,  will,  I  think,  be 
still  more  so. 

57.  How  is  the  state  of  fluidity  explained? 

58.  What  apparent  exceptions  are  there  to  the  fusibility  of  bodies? 

59.  What  is  said  respecting  such  bodies  in  other  combinations? 

60.  Why  do  not  wood,  coal,  and  other  such  bodies  liquefy? 

61.  What  remark  does  Caroline  make? 

62.  Can  any  portion  of  matter  be  annihilated? 

63.  What  is  believed  respecting  the  evaporation  of  ftll  bodies? 

E2 


54  CONVERSATIONS  ON  CHEMISTRY. 

CONVERSATION  V. 

\    » »- . 

EFFECTS  OF  CALORIC  CONTINUED. 

Fixed  and  volatile  Bodies.  Evaporation  and  Vaporization.  Soiling. 
Influence  of  Atmospheric  Pressure.  Steam.  Solution  and  Saturation.  Wol- 
laston's  Thermometer.  Water  frozen  by  vaporizing  Ether.  Distillation, 
Ignition. 

Caroline.  I  am  quite  anxious,  Mrs  B.,  to  enter  upon  the  subject  of  our 
morning's  lesson;  for  although  I  know  that  water,  and  milk,  and  other 
liquids  may  be  evaporated  by  heat,  I  have  never  had  an  idea  that  this  could 
take  place  with  bricks  and  stones.  I  am  now,  however,  prepared  to  believe 
almost  any  thing  excepting  my  senses;  but  I  confess  that  I  should  like  much 
to  see  a  block  of  marble  boiled  away, 

•Mrs  JB.  Your  reason,  my  dear  child,  was  given  to  guide  your  senses, 
by  enabling  you  to  treasure  up,  and  compare  with  each  other,  the  facts  which 
you  observe,  and  thence  to  deduce  results  with  respect  to  what  is  unseen, 
equally  certain  and  satisfactory  with  those  which  are  actually  the  objects  of 
sense.  Bricks  and  stones  may  be  fused  in  a  common  smith's  forge,  and  ana- 
logy convinces  us  that  it  is  only  the  limited  means  which  we  possess  that 
prevents  us  from  converting  them  into  vapour(l).  Those  substances  which 
we  cannot  convert  into  vapour,  are  called  fixed,  whilst  those  which  are  evapo- 
rable  are  called  volatile^}.  The  high  temperature  which  the  improvements 
in  science  have  enabled  the  chemist  to  command,  has  greatly  reduced  the 
catalogue  of  fixed  bodies,  and  it  is  not  improbable  that  those  which  remain 
are  destined  ere  long  to  yield  practical  evidence  of  the  truth  of  the  general 
law(3). 

Caroline.  As  it  is  the  attraction  of  cohesion  which  keeps  bodies  together 
in  the  mass,  and  as  heat  appears  to  be  the  agent  of  repulsion,  it  is  evident 
that  it  only  requires  an  excess  of  caloric  completely  to  counteract  this  at- 
traction, however  powerful  it  may  be(4). 

Emily.  I  can  understand  very  well  how  caloric  may  convert  liquids  into 
vapour;  but  still  there  seems  to  be  other  means  of  effecting  this,  as  we 
know  that  water  dries  away  not  only  at  the  common  temperature  of  the  at- 
mosphere, but  that  even  in  cold  frosty  weather,  clothes  which  are  hung  out 
will  still  become  dry,  although  they  may  freeze.  It  would  seem,  therefore, 
that  cold  may  evaporate  bodies  as  really,  if  not  as  rapidly,  as  heat;  or,  as 
cold  is  merely  a  negative  state,  perhaps  I  ought  rather  to  say  that  air  as 
well  as  caloric  will  convert  bodies  into  vapour(5). 

Mrs  B.  You  will  find  after  a  little  inquiry,  that  caloric  is  still  the  agent, 
whether  bodies  are  converted  into  vapour  at  natural  or  at  artificial  tempera- 
tures, and  that  the  processes  of  evaporation  and  vaporization  bear  a  strong 
analogy  to  each  other(6).  They, however,  are  very  properly  distinguished  by 
different  names;  and  though  we  do  not  always  restrict  ourselves  to  the  cor- 
rect employment  of  these  terms,  yet  the  precision  of  our  ideas  would  be 
promoted  by  greater  care  in  this  particular. 


1.  Why  cannot  bricks  and  stones  be  converted  into  vapour? 

2.  How  are  bodies  classed  in  respect  to  this  effect  of  heat? 

3.  What  is  rendered  probable  respecting  fixed  bodies? 

4.  What  reason  is  urged  in  support  of  this  opinion? 

5.  What  remark  is  made  on  evaporation  without  heat? 

6.  What  is  the  reply  to  the  objection  made? 


EFFECTS  OF  CALORIC— VAPORIZATION. 


55 


By  evaporation  we  mean  the  conversion  of  bodies  into  vapour  at  common 
temperatures,  and  by  vaporization  the  rapid  production  of  vapour  by  ebulli- 
tion^); the  only  assignable  difference  between  them  is,  that  the  former 
takes  place  quietly,  the  latter  with  the  appearance  which  we  denominate 
boiling(S).  In  every  case,  however,  all  other  circumstances  being  alike,  we 
shall  find  that  the  rapidity  of  the  process  is  precisely  proportioned  to  the 
temperature.  We  cannot  enter  fully  into  this  part  of  our  subject  until 
you  know  something  of  combined  caloric;  still  there  are  some  facts  and  ex- 
periments connected  with  it,  which  we  shall  presently  attend  to,  as  they  will 
serve  to  illustrate  the  truth,  that  vapour  is  not  produced  without  heat,  and 
consequently  that  caloric  is  the  cause  of  this  change  of  form. 

Caroline.  I  do  not  exactly  perceive  why  evaporation  should  proceed  so 
quietly  as  to  be  invisible  during  the  process,  whilst  boiling  is  accompanied 
with  so  much  agitation,  if  the  cause  producing  each  is  precisely  the  same. 

J\frs  B.  The  essential  difference  between  the  two  is,  that  in  evaporation 
the  vapour  rises  from  the  surface,  only,  of  the  liquid,  whilst  in  boiling  it  is 
produced  at  the  bottom  of  it,  where  the  heat  is  applied,  and  in  passing  up 
through  the  liquid  causes  that  agitation  which  we  call  boiling(9).  That 
evaporation  is  proportioned  to  the  extent  of  the  surface  of  a  fluid  is  proved 
by  the  fact,  that  although  the  depth  of  the  water  in  a  vessel  may  be  increased, 
its  loss  by  evaporation  will  not  be  affected  thereby;  whilst,  if  you  place  it  in 
another  vessel  in  which  the  surface  of  the  water  is  doubled,  the  evaporation 
will  be  doubled  also(10).  In  boiling,  on  the  contrary,  the  vaporization  is 
proportioned  to  the  intensity  of  the  fire,  and  the  extent  of  that  part  of  the 
vessel  which  is  exposed  to  its  action(ll). 

Emily.  Then  the  difference  seems  to  be  that  in  evaporation  the  heat  is 
in  the  air  above  the  liquid,  and  in  boiling  it  is  in 
the  fire  below  it;  and  in  this  case,  it  seems  to  me, 
that  were  we  to  apply  the  fire  over  the  water,  it 
ought  to  evaporate  only,  and  not  to  boil. 

Jlfrs  B.  Your  reasoning  is  good,  and  your  conjec- 
ture just.  It  is,  however,  as  you  know,  very  diffi- 
cult to  heat  water  from  above,  on  account  of  liquids 
being  such  bad  conductors  of  heat;  but  were  you  to 
bring  it  to  the  boiling  point,  the  consequence  would 
be  only  a  rapid  evaporation,  without  any  commo- 
tion(12). 

We  will  boil  some  water  in  this  Florence  flask,  in 
order  that  you  may  be  well  acquainted  with  the  pro- 
cess of  ebullition:  you  will  then  see,  through  the  glass, 
that  the  vapour  rises  in  bubbles  from  the  bottom. 
We  shall  make  it  boil  by  means  of  a  lamp,  which  is 
more  convenient  for  this  purpose  than  the  chimney 
fire. 

Emily.  I  see  some  small  bubbles  ascend,  and  a 
great  many  appear  all  over  the  inside  of  the  flask; 
does  the  water  begin  to  boil  already? 

JHrs  B.  No:  what  you  now^see  are  bubbles  of  air, 
which  were  either  dissolved  in  the  water,  or  attached 


7.  What  is  intended  by  the  terms  evaporation  and  vaporization? 

8.  What  is  the  sensible  difference  between  them? 

9.  What  produces  the  agitation  in  boiling? 

10.  To  what  is  evaporation  proportioned  and  how  is  this  shown? 

11.  To  what  Is 'vaporization  proportioned? 

12.  What  would  be  the  effect  of  applying  heat  above  a  fluid? 


56  CONVERSATIONS  ON  CHEMISTRY. 

to  the  inner  surface  of  the  flask,  and  which,  being  rarefied  by  the  heat,  ascend 
in  the  water(13). 

Emily.  But  the  heat  which  rarefies  the  air  inclosed  in  the  water  must 
rarefy  the  water  at  the  same  time;  therefore,  if  it  could  remain  stationary  in 
the  water  when  both  were  cold,  I  do  not  understand  why  it  should  not  when 
both  are  equally  heated. 

J\frs  J$.  Air  being  much  less  dense  than  water,  is  more  easily  rarefied. 
The  former,  therefore,  expands  to  a  great  extent,  whilst  the  latter  continues 
to  occupy  nearly  the  same  space  ;  for  the  water  dilates  out  very  little,  com- 
paratively, without  changing  its  state  and  becoming  vapour(l4).  Now  that 
the  water  in  the  flask  begins  to  boil,  observe  what  large  bubbles  rise  from 
the  bottom  of  it. 

Emily.  I  see  them  perfectly;  but  I  wonder  that  they  have  sufficient  pow- 
er to  force  themselves  through  the  water. 

Caroline.  They  must  rise,  you  know,  from  their  specific  levity;  just  as 
hubbies  of  air  rise,  when  we  blow  through  a  tube  into  a  glass  of  water(15). 
How  rapidly  they  now  pass  up,  as  the  heat  increases  from  raising  the  lamp. 
A  thermometer  would,  I  should  apprehend,  now  stand  above  212°. 

JMrs  JB.  By  no  means:  when  the  heat  applied  is  increased,  a  greater 
quantity  of  vapour  is  produced,  but  the  temperature  remains  the  same.  The 
extra  heat  is  carried  off  by  the  vapour,  and  whilst  this  is  allowed  to  escape 
freely,  you  cannot,  by  the  most  intense  fire,  increase  the  heat  of  the  wa- 
ter(16).  And  the  same  is  true  of  other  liquids;  for  although  in  their  boiling 
points  they  vary  one  from  another,  yet  each  remains  unifoi-mly  the  same, 
under  the  same  atmospheric  pressure(17).  Sulphuric  ether  boils  at  96°, 
alcohol  at  173°,  water  at  212°,  oil  of  turpentine  at  316°,  and  mercury  re- 
quires to  be  raised  to  660°,  which  is  about  the  temperature  at  which  bodies 
begin  to  appear  luminous  in  the  dark(18). 

Caroline.  From  what  you  said  just  now,  I  infer  that  the  boiling  point  is 
different  as  the  pressure  of  the  atmosphere  varies;  but  if  this  be  the  case, 
the  thermometer  cannot  always  stand  at  the  same  degree  in  boiling  water, 
and  of  course  these  instruments  must  vary  from  each  other  as  they  are  made 
at  different  seasons(19).  Without  doubting  the  fact,  I  am  unable  to  perceive 
how  a  variation  in  the  weight  of  the  air  should  occasion  this  difference  in 
the  boiling  point  cf  liquids. 

Mrs  Ji.  You  are  aware  that  the  atmosphere  presses  with  a  force  equal 
to  15  pounds  on  every  square  inch  of  the  earth's  surface,  and  this  pressure 
must  necessarily  tend,  like  the  attraction  of  cohesion,  to  keep  the  particles 
of  bodies  together;  and,  of  course,  the  less  this  pressure,  the  more  readily 
will  the  particles  separate.  In  the  boiling  of  a  liquid,  therefore,  there  are, 
ordinarily,  these  two  forces  to  overcome,  the  power  of  attraction,  and  atmos- 
pheric pressure(20).  Care  is  taken  to  allow  for  any  variation  of  this  pres- 
sure which  may  exist  at  the  time  when  a  thermometer  is  made(21).  You 
may  judge  how  necessary  this  is  when  I  tell  you  that  all  liquids  have  their 
boiling  point  lowered  about  140°,  when  the  pressure  of  the  atmosphere  is 


13.  What  experiment  is  given,  and  what  the  first  appearance? 

14.  How  is  the  separation  of  the  air  effected? 

15.  What  causes  the  bubbles  of  steam  to  rise? 

16.  WThat  is  the  effect  of  increasing  the  heat? 

17.  What  is  remarked  of  the  boiling  of  different  liquids? 

18.  Give  some  examples  of  this  difference. 

19.  What  effect  does  a  difference  in  atmospheric  pressure  produce? 

20.  How  is  this  accounted  for? 

21.  Is  this  noticed  in  making  a  thermometer? 


EFFECTS  OF  CALORIC— VAPORIZATION. 


57 


entirely  removed (22):  water  would  consequently,  under  such  circum- 
stances, boil  in  the  hollow  of  the  hand,  as  it  would  require  but  72°,  alcohol 
at  33°,  and  ether  at  44°  below  the  freezing  point(23). 

Emily.  Cannot  we  try  this  by  means  of  the  air  pump?  I  should  like  very 
much  to  see  a  liquid  boil,  that  was  colder  than  ice. 

Mrs  B.  You  shall  see  this,  but  I  will  first  show  you,  by  means  of  the  flask 
of  boiling  water,  the  effect  of  diminished  pressure  in  promoting  ebullition. 
Before  the  water  boiled,  the  upper  part  of  the  flask  was  filled  with  air,  but 
the  steam  has  forced  this  out,  and  now  occupies  its  place.  I  will  carefully 
cork  the  flask,  remove  it  from  the  lamp,  and  tie  a  piece  of  wet  bladder  over  the 
cork,  so  as  completely  to  exclude  the  air.  There  is  now  an  atmosphere  of 
steam  which  presses  upon  the  contained  water;  if,  by  the  application  of  cold, 
this  steam  be  condensed,  the  water  will  again  boil.  For  this  purpose  I  invert 
the  flask,  place  it  on  a  stand,  and  apply  to  it  a 
piece  of  ice,  or  a  sponge  dipped  into  cold  water. 
sThis  you  see  renews  the  ebullition,  and,  provided 
the  flask  has  been  closely  stopped,  and  the  air 
^' perfectly  excluded,  it  will  continue  to  do  so  when 
the  water  is  so  cool  that  the  flask  may  be  held  in 
the  hand  without  inconvenience.  If,  on  the  con- 
trary, I  pour  boiling  water  upon  it,  the  ebullition 
will  instantaneously  cease(24).  This  experiment 
serves  also  to  exemplify  the  great  difference  be- 
tween those  aeriform  bodies  which  are  permanent- 
ly elastic,  and  those  which  are  not  so.  The  for- 
mer contract  in  bulk  when  cooled?  but  the  latter 
are  condensed,  change  their  form,  and  become 
liquids(25). 

Caroline.  I  think  that  I  understand  the  expe- 
riment perfectly.  The  steam,  whilst  such,  acts 
like  the  atmosphere  and  presses  upon  the  water. 
The  cold  takes  off  this  pressure  by  condensing  the 
steam,  whilst  the  hot  water  restores  it  in  its  elas- 
tic state,  and  consequently  suppresses  the  boil- 
ing(26). 

Emily.  But  if  there  was  steam  in  the  flask  over  the  water,  why  did  we 
not  see  it.  We  saw  it  plainly  as  it  escaped  from  the  flask  whilst  over  the 
lamp,  as  we  always  do  from  the  spout  of  a  tea  kettle? 

Mrs  B.  You  are  mistaken;  that  which  you  see  is  not  steam,  but  minute 
drops  of  water,  produced  by  the  condensation  of  the  steam  in  the  cool  at- 
mosphere. Steam  is  as  invisible  as  air.  Your  error,  however  is  a  very 
natural  one,  as  that  which  is  seen  is  usually  called  steam(27). 

Emily.  Now  then  I  can  account  for  what  I  have  often  noticed,  that  when 
we  look  close  to  the  spout  of  a  boiling  kettle,  the  steam  appears  quite  trans- 
parent, whilst  it  is  cloudy  at  a  little  distance  off(28). 

Mrs  B.  This  appearance  may  serve  to  exemplify  the  difference  be- 
tween SOLUTION  and  mere  mixture.  When  the  steam  first  issues  it  is 
completely  dissolved  by  the  caloric,  and  is  consequently  invisible.  When 


22.  What  is  the  whole  amount  of  the  effect  of  atmospheric  pressure? 

23.  ,What  would  be  the  effect  upon  water,  alcohol,   and  ether? 

24.  Detail  the  experiment  with  the  boiling  water,  and  its  object. 

25.  What  does  this  exemplify  besides  the  effect  of  pressure? 

26.  Give  Caroline's  explanation. 

27.  Is  steam  visible;  and  what  is  that  which  is  usually  so  called? 

28.  What  may  be  observed  in  a  boiling  tea  kettle? 


58  CONVERSATIONS  ON  CHEMISTRY.       . 

cooled  and  partially  condensed,  the  minute  drops  of  water,  which  are 
mixed  with  the  air,  become  visible;  but  then  again  as  they  pass  into  the 
room,  they  acquire  a  fresh  portion  of  caloric  from  the  atmosphere,  are  again 
dissolved,  and  therefore  no  longer  seen(29). 

Caroline.  Solution  then  is  a  mode  of  destroying  the  attraction  of  aggre- 
gation(30). 

Mrs  B.  Undoubtedly.  The  two  principal  solvent  fluids  are  -water  and 
caloric(3l).  You  may  have  observed  that  if  you  dissolve  salt  in  water  it 
becomes  totally  invisible,  and  the  water  remains  ck-ar  and  transparent  as 
before;  yet  though  the  union  of  these  two  bodies  appears  so  perfect,  it  is  not 
produced  by  any  chemical  combination  which  permanently  alters  the  nature 
of  either  of  them;  for  if  you  were  to  separate  them  by  evaporating  the  water, 
you  would  find  the  salt  in  the  same  state  as  before.  You  are  not,  however, 
to  conclude  that  there  is  in  this  case  no  chemical  union  at  all,  but  merely 
that  it  is  one  which  is  easily  destroyed(32). 

Emily.  I  suppose  that  water  is  a  solvent  for  solid  bodies,  and  caloric  for 
liquids? 

Mrs  B.  Liquids,  of  course,  can  only  be  converted  into  vapour  by  caloric; 
but  the  solvent  power  of  this  agent  is  not  at  all  confined  to  that  class  of 
bodies.  A  great  variety  of  solid  substances  are  dissolved  by  heat;  thus  me- 
tals, which  are  insoluble  in  water,  can  be  dissolved  by  intense  heat,  being 
first  fused  or  converted  into  a  liquid,  and  then  rarefied  into  an  invisible  va- 
pour. Many  bodies  yield  to  either  of  these  solvents(33). 

Caroline.  And  that,  no  doubt,  is  the  reason  why  hot  water  will  dissolve 
most  bodies  much  better  than  cold  water. 

Mrs  B.  It  is  so.  Caloric  may,  indeed,  be  considered  as  having  in  every 
instance,  some  share  in  the  solution  of  a  body  by  water,  since  water,  how- 
ever low  its  temperature  may  be,  always  contains  more  or  less  caloric(34). 

Emily.  Then,  perhaps,  water  owes  its  solvent  power  merely  to  the  ca- 
loric contained  in  it. 

Mrs  B.  That,  probably,  would  be  carrying  the  speculation  too  far.  I 
should  rather  think  that  water  and  caloric  unite  their  efforts  to  dissolve  a 
body,  and  that  the  difficulty  or  facility  of  effecting  this,  depends  both  on  the 
degree  of  attraction,  or  aggregation,  to  be  overcome,  and  on  the  arrangement 
of  the  particles  which  are  more  or  less  disposed  to  be  divided  and  penetra- 
ted by  the  solvent(35). 

Emily.     But  have  not  all  liquids  the  same  solvent  power  as  water? 

Mrs  B.  The  solvent  power  of  other  liquids  varies  according  to  their 
nature,  and  that  of  the  substances  submitted  to  their  action.  Some  of  them, 
particularly  the  acids,  dissolve  the  metals,  and  in  so  doing  are  themselves, 
in  many  cases,  decomposed.  A  great  variety  of  new  substances  is  thus  form- 
ed(36);  but  these  more  complicated  operations  we  must  consider  in  another 
place,  and  confine  our  attention,  at  present,  to  the  solutions  by  water  and 
caloric. 

Caroline.  But  there  is  a  variety  of  substances  which,  when  dissolved  in 
water,  make  it  thick  and  muddy,  and  destroy  its  transparency. 

Mrs  B.     In  this  case,  it  is  not  a  solution,  but  simply  a  mixture.     I  shall 


29.  How  does  this  exemplify  the  difference  between  solution  and  mixture? 

30.  What  does  solution  destroy? 

31.  What  are  the  principal  solvents? 

32.  What  is  remarked  on  a  solution  of  salt  in  water? 

33.  What  general  remarks  are  made  upon  water  and  heat  as  solvents? 

34.  Does  caloric  appear  to  be  concerned  in  solution  generally? 

35.  What  appears  to  be  the  joint  action  of  water  and  caloric? 

36.  What  is  said  of  other  solvents? 


EFFECTS  OF  CALORIC— SOLUTION.  59 

show  you  the  difference  between  a  solution  and  a  mixture,  by  putting  some 
common  salt  into  one  glass  of  water,  and  some  powder  of  chalk  into  ano- 
ther. Both  these  substances  are  white,  but  their  effect  on  the  water  will  be 
very  different. 

Caroline.  Very  different,  indeed:  the  salt  entirely  disappears,  and  leaves 
the  water  transparent,  whilst  the  chalk  changes  it  into  an  opake  liquid 
like  milk. 

•Mrs  J3.  One  character  of  a  solution  is  transparency.  It  need  not  be  co- 
lourless, as  there  are  solutions  of  almost  every  variety  of  colour,  but  they 
are  all  transparent(37).  A  powder,  however  fine  it  may  be,  will  render  a 
fluid  opake,  if  it  remains  undissolved,  and  will,  most  commonly,  be  preci- 
pitated, or  fall  to  the  bottom,  if  the  fluid  be  allowed  to  remain  at  rest. 
This  is  never  the  case  with  a  solution,  although  the  specific  gravity  of  the 
article  dissolved  be  much  greater  than  that  of  the  fluid  with  which  it  has 
combined(38). 

Caroline.  A  portion  of  salt  which  I  have  added  to  the  water  remains 
undissolved,  although  I  have  continued  to  stir  it  for  a  long  time;  yet  at  first 
it  dissolved  very  quickly. 

Mrs  B.  There  is  a  certain  quantity  of  a  substance  which  its  solvent  can 
take  up:  when  this  quantity  is  dissolved,  the  point  of  saturation  is  attained, 
and  we  have  what  is  denominated  a  saturated  solution.  In  the  present  in- 
stance the  water  is  saturated,  and  has  no  more  power  to  dissolve  an  addi- 
tional portion  of  salt  than  of  sand(39). 

Emily.  Is  not  the  air  a  solvent  for  water?  In  a  windy  day  water  dries 
away  with  much  greater  rapidity  than  in  still  weather. 

Mrs  B.  It  was  formerly  supposed,  from  the  case  you  have  stated,  that 
water  was  dissolved  by  the  air;  but  it  appears  from  more  accurate  observa- 
tions, that  the  solvent  power  of  the  atmosphere  depends  solely  upon  the 
caloric  contained  in  it.  The  motion  of  the  air  removes  that  which  has 
been  dissolved,  which  otherwise  would  prevent  all  further  solution.  You 
will  presently  see  that  by  removing  the  atmosphere,  the  quantity  of  water 
dissolved  will  be  increased(40). 

Do  you  recollect  upon  what  principle  the  barometer  is  used  for  measur- 
ing the  altitude  of  mountains,  or  the  height  to  which  a  balloon  ascends? 

Caroline.  Perfectly  well.  As  you  ascend  the  quantity  of  air  above  you 
decreases,  and  it  must  consequently  become  less  and  less  dense,  and  press 
with  decreasing  force.  The  mercury  in  the  barometer,  therefore,  descends 
in  proportion  to  the  elevation  of  the  place  to  which  it  is  taken(41).  No\r 
let  me  tell  you  why  you  made  that  inquiry:  it  was  to  show  that  water  must 
boil  at  a  lower  temperature  in  such  situations;  was  it  not(42)? 

Mrs  B.  You  have  guessed,  or  rather  judged  right,  and  the  late  Rev.  Mr 
Wollaston  showed  how,  upon  this  principle,  the  thermometer  might  be 
substituted  for  the  barometer  in  measuring  heights.  He  made  a  thermo- 
meter in  which  every  degree  on  Fahrenheit's  scale  was  divided  into  one 
thousand  parts;  and  such  was  its  extreme  sensibility  that  it  evinced  a  differ- 
ence in  the  heat  of  boiling  water  in  a  vessel  placed  first  on  the  floor,  and 


37.  How  may  the  difference  between  mixture  and  solution  be  shown,  and 
what  is  a  uniform  character  of  solution? 

38.  What  further  difference  is  noticed? 

39.  What  are  saturation,  and  a  saturated  solution? 

40.  How  is  water  dissolved  in  the  atmosphere? 

41.  How  does  the  barometer  operate  in  measuring  altitudes? 

42.  How  must  water  be  affected  in  elevated  situations? 


60 


CONVERSATIONS  ON  CHEMISTRY. 


afterwards  upon  a  table.  The  most  perfect  and  delicate  barometer  fall* 
very  far  short  of  this(43). 

Emily,  I  am  glad  to  see  the  air  pump  upon  the  table,  and  the  bottle  of 
ether,  which  is  to  boil  over  a  fire  as  cold  as  ice.  After  seeing  ice  cause  water 
to  boil,  I  shall  not  be  surprised  to  see  it  produce  the  same  effect  upon 
ether,  which  is  so  much  more  volatile. 

Mrs  B.  You  will  find  them  to  be  very  different  operations:  in  the  for- 
mer experiment  the  ice  produced  the  boiling;  in  the  present  you  will  find 
the  boiling  produce  the  ice.  Observe  how  suddenly  the  ether  in  this  phial 
will  be  converted  into  vapour,  by  means  of  the  air  pump.  See  with  what 
rapidity  the  bubbles  will  ascend,  as  1  take  off  the  pressure  of  the  atmos- 
phere. To  show  this  I  open  the  vial,  place  it  under  a  receiver,  and  ex- 
haust the  air(44). 

Caroline.    It  positively  boils:  how  singular  to  see  a  liquid  boil  without  heat ! 

Air  Pump  with  Receiver  and  Apparatus  for  freezing  Water. 


Mrs  B.  Now  I  will  place  the  phial  of  ether  in  this  small  cylindrical 
glass,  which  it  so  nearly  fits  as  to  leave  only  a  small  space  between  them, 
which  I  fill  with  water;  and  in  this  state  I  put  it  again  under  the  receiver. 
You  will  observe,  as  I  exhaust  the  air  from  it,  that  whilst  the  ether  boils,  the 
water  freezes(45). 

Caroline.  It  is  indeed  wonderful  to  see  water  freeze  in  contact  with  a 
boiling  fluid! 

Emily.  I  am  at  a  loss  to  conceive  how  the  ether  can  pass  to  the  state  of 
vapour,  without  an  addition  of  caloric.  Does  it  not  contain  more  caloric  in 
a  state  of  vapour,  than  as  a  liquid? 

Mrs  B.  It  certainly  does;  for  though  it  is  the  pressure  of  the  atmosphere 
which  keeps  it  in  the  state  of  a  liquid,  it  cannot  pass  into  the  aeriform  state 
without  absorbing  a  quantity  of  caloric. 

Emily.  You  have  therefore,  .two  difficulties  to  explain,  Mrs  B.  First, 
whence  the  ether  obtains  the  caloric  necessary  to  convert  it  into  vapour, 
when  it  is  relieved  from  the  pressure  of  the  atmosphere;  and,  secondly,  what 
is  the  reason  that  the  water,  in  which  the  bottle  of  ether  stands,  is  frozen? 


43.  How  did  the  Rev.  Mr  Wollaston  exemplify  this? 

44.  How  may  ether  be  made  to  boil  by  means  of  the  air  pump? 

45.  By  what  arrangement  may  water  be  frozeu? 


EFFECTS  OF  CALORIC— EVAPORATION.        61 

Caroline.  Now  I  think  I  can  answer  both  these  questions,  and  so  kill  two 
birds  with  one  stone.  The  ether  obtains  the  addition  of  caloric  required 
from  the  water  in  the  glass;  and  the  loss  of  caloric  which  the  latter  sustains, 
is  the  occasion  of  its  freezing(46). 

Emily.  This  I  understand  now  very  well;  but  if  the  water  freezes  in 
consequence  of  yielding  its  caloric  to  the  ether,  the  equilibrium  of  heat 
must,  in  this  case,  be  totally  destroyed.  Yet  we  have  been  told  that  the  ex- 
change of  caloric  between  two  bodies  of  equal  temperature,  is  always 
equal;  how,  then,  is  it  that  the  water,  -which  was  originally  of  the  same 
temperature  as  the  ether,  gives  out  caloric  to  it,  till  the  water  is  frozen 
and  the  ether  made  to  boil? 

Mrs  B.  I  had  anticipated  that  you  would  make  these  objections,  but 
can  assure  you  that  the  equilibrium  of  temperature  is  not  destroyed;  for  were 
we  to  place  one  thermometer  in  the  ether,  and  another  in  the  water,  and 
observe  them  during  the  experiment,  we  should  find  that  they  would  descend 
equally;  that  both  thermometers  would  indicate  the  same  temperature, 
though  one  of  them  were  in  a  boiling,  the  other  in  a  freezing  liquid(47). 

Emily.  The  ether,  then,  becomes  colder  as  it  boils.  This  is  so  con- 
trary to  common  experience,  that  I  confess  it  astonishes  me  exceedingly. 

Caroline.  It  is,  indeed,  a  most  extraordinary  circumstance.  But  pray 
how  do  you  account  for  it? 

•Mrs  B.  I  cannot  satisfy  your  curiosity  at  present,  but  must  defer  the 
explanation,  with  that  of  some  othejr  facts  which  we  have  partially  noticed, 
until  our  conversation  on  combined  caloric,  or  latent  heat.  The  fact,  how- 
ever, of  the  intense  cold  produced  by  the  evaporation  of  ether,  will  be  ren- 
dered sensible  by  your  allowing  a  drop  or  two  to  fall  upon  the  back  of 
your  hand,  from  the  bottle. 

Caroline.  Oh,  how  cold!  and  it  is  scarcely  on  before  it  is  dry.  I  had 
not  the  most  remote  idea  of  the  intensity  of  the  sensation  it  would  produce, 
as  the  bottle  appeared  not  to  be  colder  than  the  other  articles  in  the  room(48). 

Mrs  B.  The  cold  is  entirely  the  effect  of  the  evaporation,  and  all 
evaporation  is  attended  with  a  similar  result.  The  intensity  of  the  cold  must 
of  course  be  proportionate  to  the  rapidity  of  the  process;  and  therefore  the 
most  volatile  fluid  must  produce  the  most  striking  effect(49). 

Emily.  Pray,  Mrs  B.,  what  would  become  of  the  water  in  the  ocean, 
and  in  our  rivers,  were  the  pressure  of  the  atmosphere  removed?  It  appears 
to  me  that  it  would  all  boil  away;  at  all  events  this  must  be  the  case  iu 
tropical  climates,  where  the  heat  is  generally  above  88°. 

Mrs  B.  This  use  of  the  atmosphere  affords  another  example  of  the  pro- 
vidential care  and  wisdom  of  the  Creator,  and  ought  to  operate  as  an  ad- 
ditional incentive  to  the  study  of  his  works,  in  which  we  find  BO  many 
important  purposes  effected  by  means  the  most  simple.  The  atmosphere 
is  necessary  to  sustain  life,  and  it  obviously  answers  numerous  other  valu- 
able ends;  but  who,  unless  informed  by  science,  would  ever  have  dreamt 
that  the  existence  of  the  ocean,  and  of  every  stream  of  water,  depends  upon 
its  pressure  ?  It  is  a  fact,  however,  that,  in  every  climate,  but  for  this  force, 
the  whole  of  them  -would  be  soon  converted  into  watery  vapour,  and  form  an 
aqueous  atmosphere,  surrounding  the  earth,  but  answering  none  of  those 
purposes  which  are  requisite  to  render  it  habitable(SO). 


46.  Upon  what  principle  does  this  depend? 

47.  What  will  be  the  respective  temperatures  of  the  ice  and  ether? 

48.  What  sensation  will  be  produced  if  ether  be  dropped  on  the  hand? 

49.  From  what  cause  doijs  the  cold  produced  arise? 

50.  What  would  become  of  the  waters,   were  atmospheric  pressure 
removed? 

F 


62  CONVERSATIONS  ON  CHEMISTRY. 

Caroline.  The  little  that  we  have  learned,  Mrs  B.,  by  your  persevering 
kindness,  would  be  a  rich  reward  for  the  labour  of  years;  and  I  am  sure 
that  the  delight  which  it  has  already  afforded  us  will  be  an  effectual  motive  to 
perseverance.  We  are  indeed  most  grateful  to  you  for  directing  us  to  sources 
of  enjoyment  so  far  superior  to  what  is  usually  denominated  pleasure. 

Mrs  B.  Before  dismissing  the  subject  of  vaporization,  there  is  a  che- 
mical process,  the  nature  and  object  of  which  you  should  fully  understand, 
and  that  is  distillation.  The  principal  object  of  this  process  is  to  separate 
and  collect  the  more  volatile  of  two  fluids  which  may  be  mixed  together. 
This  operation  is  founded  upon  the  difference  in  the  boiling  points  of  differ- 
ent fluids,  in  consequence  of  which,  when  heat  is  applied  to  them  in  their 
mixed  state,  one  of  them  will  evaporate  at  a  lower  temperature  than  the 
other(51). 

Caroline.  I  have  seen  them  distilling  spirits,  which  I  believe  was  obtained 
from  rye,  and  have  understood  that  it  can  be  procured  from  many  other 
articles. 

J\frs  S.  All  the  liquors  called  vinous,  such  as  the  various  kinds  of 
wine,  beer,  cider,  &c.  contain  a  spirituous  liquid  called  alcohol,  or  spirits  of 
wine,  but  mixed  with  water,  and  other  matters(52).  When  heated,  the  alco- 
hol first  rises  in  vapour,  and  were  this  evaporation  to  be  carried  on  in  an 
open  vessel,  the  vapour  would  fly  off  and  be  lost.  The  apparatus  usually 
employed  is  called  an  alembic,  or  still,  and  is  generally  made  of  copper. 
I  will  show  you  a  drawing  of  one  presently;  but  a  common  tea  kettle  will 
afford  you  some  idea  of  its  nature.  Suppose  that  the  liquid  to  be  distilled 
•was  put  into  one  of  these  vessels,  with  the  lid  so  secured  that  steam  could 
not  escape,  excepting  through  the  spout,  that  a  long  tube  was  fastened  to  the 
spout,  and  this  tube  made  to  pass  through  a  vessel  of  cold  water;  any  va- 
pour which  passed  into  the  tube  would  be  condensed,  assume  the  liquid 
form,  and  fall  in  drops  out  of  the  tube(53). 

Emily.  And  if  we  were  to  put  a  vinous  liquor  into  such  a  kettle,  and  heat 
it,  the  spirit  would  rise  first,  and  leave  the  watery  part  behind. 


Common  Alembic,  or  Still  for  Spirits. 


N 

Mrs  B.    Yes;  but  it  would,  in  the  first  instance,  be  accompanied  by  a  con- 
siderable portion  of  the  water,  from  which  it  must  be  separated  by  redis- 


51.  What  is  the  object  of  distillation,  and  upon  what  does  it  depend? 

52.  What  is  contained  in  vinous  liquors  of  every  description? 

53.  What  is  an  alembic,  or  still,  and  what  does  it  resemble? 


EFFECTS  OF  CALORIC— DISTILLATION. 


63 


tillation  or  rectification,  as  it  is  called(54).  This  is  a  drawing  of  a  still. 
A,  is  the  body  of  the  still,  which  is  to  be  enclosed  in  a  furnace.  B,  the  head, 
or  capital.  C,  the  beak  or  spout.  D,  the  worm,  which  is  a  long  metal  tube 
enclosed  in  the  refrigerator,  which  is  a  tub  or  cistern  kept  full  of  cold 
water.  E,  a  vessel  for  receiving  the  spirits  which  have  been  condensed  in 
passing  through  the  worm(55).  It  is  by  an  apparatus  of  this  description, 
that  the  various  kinds  of  spirituous  liquors  are  obtained,  such  as  brandy, 
rum,  gin,  whiskey,  and  a  variety  of  others. 

Caroline.  As  spirit  is  converted  into  vapour  at  a  temperature  so  far  be- 
low that  of  water,  is  it  not  possible,  by  regulating  the  heat,  to  obtain  the 
spirit  pure  at  once  without  rectification? 

Mrs  B.  By  no  means.  When  two  fluids  of  different'volatility  are  com- 
bined together,  they  modify  each  other's  properties.  When  the  more  vola- 
tile of  the  two  is  driven  off,  it  will,  in  consequence  of  the  force  of  the  affi- 
nity by  which  they  are  united,  carry  with  it  a  certain  portion  of  that  which 
is  less  so.  This  is  the  case  even  with  solids,  there  being  very  few  with 
which  water  combines  which  are  not,  in  part,  converted  into  vapour,  when 
the  water  is  driven  off  by  heat(56). 

Glass  Alembic  for  Distillation. 


[A,  body  of  the  Alembic.     B,  the  head.     C,  the  beak  for  conducting  the 
condensed  fluid  into  the  glass.] 

In  distilling  in  the  small  way,  an  operation  which  we  shall  have  frequent 
occasion  to  perform,  the  chemist  sometimes  uses  an  alembic  of  glass,  such  as 
I  now  have  over  the  lamp.  By  keeping  the  head  and  beak  cool,  the  vapour 
which  rises  is  condensed,  and  drops  out  in  the  liquid  form.  Such  an  appa- 
ratus is  useful  on  account  of  the  smallness  of  the  quantity  which  may  be 
operated  upon  by  it.  The  progress  of  the  experiment  may  be  seen,  and 


54.  What,  is  rectification,  and  why  is  it  necessary? 

55.  Describe  the  common  still  and  its  refrigerator. 

56.  Why  may  not  pure  spirit  be  at  once  obtained? 


64 


CONVERSATIONS  ON  CHEMISTRY. 


substances  which  would   destroy  the  metals,   are  thus  prepared   or  em- 
ployed^?). 

What  is  called  a  retort  is  the  kind  of  still  most  commonly  used  by  the 
chemist.  When  the  vapour  which  passes  over  is  to  he  condensed,  the  beak, 
or  mouth  of  the  retort,  is  fitted  into  a  receiver,  which  may  be  kept  cold 
by  immersion  in  cold  water,  or  in  some  other  way (5 8). 


Retort,  Receiver,  and  Lamp. 


Retort  and  lamp. 


Receiver  and  stand. 


I  had  some  idea  of  distillation  before,  but  by  no  means  a  clear 
one.  I  always  thought  that  there  was  something  complex  and  mysterious 
about  the  process,  instead  of  that  perfect  simplicity  which  I  now  see  in  it. 

JWrs  B.  The  effects  of  caloric,  which  have  formed  the  subject  cf  the  pre- 
sent conversation,  form  a  regular  series,  and  generally  take  place  in  uniform 
succession.  Expansion,  liquefaction,  and  vaporization,  appear  to  be  pro- 
duced in  obedience  to  one  general  law.  There  is,  however,  another  effect  of 
caloric  apparently  altogether  disconnected  with  them,  and  that  is  IGNTTIOIT, 
or  incandescence,  by  which  is  meant  that  emission  of  light  which  is  produced 
in  bodies  at  a  very  high  temperature;  all  substances  being  capable  of  becom- 
ing red  hot,  and  of  emitting  light,  as  well  as  heat(59). 

Emily.  You  mean,  I  suppose,  that  light  which  is  produced  by  a  burn- 
ing body. 

Mrs  B.  No;  ignition  is  quite  independent  of  combustion.  Clay,  chalk, 
and  indeed  all  incombustible  substances  may  be  made  red  hot.  When  a  body 
burns,  the  light  emitted  is  the  effect  of  a  chemical  change  which  takes  place, 
whilst  ignition  is  the  effect  of  caloric  alone,  and  no  other  change  than  that 
of  temperature  is  produced  in  the  ignited  body.  By  combustion  a  body  is 
decomposed,  and  it  therefore  can  be  performed  on  the  same  substance  but 
once,  whilst  ignition  can  be  induced  in  the  same  body  any  number  of  times. 
Combustion  requires  the  presence  of  air,  ignition  that  of  heat  only(60). 

All  solid  bodies,  and  some  liquids,  are  susceptible  of  ignition,  or  in  other 
words,  of  being  heated  so  as  to  become  luminous;  and  it  is  remarkable  that 
in  a  situation  perfectly  dark,  this  takes  place  at  the  same  temperature  in  all 
bodies,  that  is  somewhere  between  600  and  800  degrees  of  Fahrenheit's 
scale(61). 


57.  Describe  the  glass  alembic. 

58.  What  is  most  commonly  used  for  distilling  by  the  chemist? 

59.  What  is  ignition  or  incandescence? 

60.  What  is  the  difference  between  this  light,  and  that  from  combustion? 
61  At  what  temperature  does  it  occur,  and  in  what  bodies? 


COMBINED  CALORIC— SPECIFIC  HEAT.  65 

Emily.  But  how  can  liquids  attain  so  high  a  temperature,  without  being 
converted  into  vapour? 

Mrs  JB.  It  would  certainly  be  extremely  difficult  to  bring  the  more  vola- 
tile liquids  to  such  a  temperature,  and  it  could  only  be  done  by  confining 
them  in  a  vessel  of  immense  strength,  in  order  to  be  able  to  resist  the  elasticity 
of  vapour  so  highly  heated.  But  if  they  were  so  confined,  and  this  vessel 
then  heated  to  ignition,  its  contents  must  be  so  also(62). 

There  are  many  speculations  with  respect  to  the  sources  of  the  light  of 
ignition,  but  as  little  that  is  satisfactory  is  known  on  this  point,  it  would  be 
unwise  in  us  to  discuss  it.  At  our  next  meeting  we  shall  converse  about 
latent  heat,  which  is  a  subject  sufficiently  important  to  claim  your  undivided 
attention. 


CONVERSATION  VI. 

ON  COMBINED   CALORIC,    COMPREHENDING  SPECIFIC  AND 
LATENT  HEAT. 

Bodies  have  different  Capacities  for  Heat.  Proof  by  different  Metals. 
•Mercury  and  Water  compared.  Rarefaction  and  Condensation.  Distinc- 
tion bet-ween  Specific  and  Latent  Heat.  Change  of  Form.  .Mixture  of 
heated  Water  and  Ice.  Heat  latent  in  Steam  and  Vapour.  Condensation 
of  Steam.  Snow  and  Salt  as  a  freezing  Mixture. 

Mrs  JB.  We  are  now  to  examine  the  other  modifications  of  caloric,  but 
in  order  to  enable  you  to  under  stand  them,  it  will  be  necessary  to  enter  into 
some  previous  explanations. 

It  has  been  discovered  by  modern  chemists,  that  bodies  which  differ  in  their 
natures  from  each  other,  though  heated  to  the  same  temperature,  do  not  con- 
tain the  same  quantity  of  caloric(l). 

Caroline.  How  could  that  be  ascertained?  Have  you  not  told  us  that 
the  absolute  quantity  of  caloric  which  bodies  contain  was  entirely  unknown. 
to  us? 

Mrs  B.  True,  but  at  the  same  time  I  said  that  we  were  enabled  to  form 
a  judgment,  by  means  of  the  thermometer,  of  the  proportion  in  which  it  en- 
tered into  bodies  between  certain  temperatures.  This,  however,  is  true  as 
respects  any  one  species  of  matter  only,  as  water  for  example.  Thus,  if  we 
raise  a  given  portion  of  the  fluid  10°,  it  will  require  an  equal  addition  of  ca- 
loric to  raise  it  another  10°;  but  it  is  found  that,  in  order  to  raise  the  tem- 
perature of  different  bodies  the  same  number  of  degrees,  different  quantities 
of  caloric  are  required  for  each  of  them.  If,  for  instance,  you  place  a  pound 
of  lead,  a  pound  of  chalk,  and  a  pound  of  milk,  in  a  hot  oven,  they  will  be 
gradually  heated  to  the  temperature  of  the  oven;  but  the  lead  will  attain  it 
first,  the  chalk  next,  and  the  milk  last,  and  they  will  be  found  to  have  absorb- 
ed from  the  oven  very  different  quantities  of  caloric(2). 

Caroline.  I  do  not  see  that  one  substance  taking  longer  time  than  ano- 
ther to  become  heated,  proves  that  more  caloric  is  required,  to  produce  this 
effect,  in  one  case  than  in  the  other;  as  such  a  difference  must  necessarily 
arise  from  the  difference  in  the  conducting  power  of  the  bodies.  The  lead, 


62.  In  what  way  might  a  fluid  be  made  red  hot> 

1.  What  has  been  discovered  respecting  the  caloric  contained  in  bodies? 

2.  What  exemplifications  are  given  of  this  fact  ? 

F2 


66  CONVERSATIONS  ON  CHEMISTRY. 

for  instance,  conducts  so  much  better  than  either  of  the  others,  that  it  must, 
of  course,  be  the  most  quickly  heated(3). 

Jtfrs  B.     Your  reasoning  is  very  good,  as  far  as  conducting  power  is  con- 
eerned;  but  facts,  as   established  by  decisive  experiments,   overturn  your 
theory,  and  leave  no  doubt  that  the  quantity  of  caloric  -which  enters  into  va- 
rious substances  to  produce  in  them  the  same  thermometrie  effect,  is  very 
different;  and  hence  they  are  said  to  possess  different  capacities  for  caloric. 
Caroline.     What  do  you  mean  by  the  capacity  of  a  body  for  caloric? 
Mrs  B.     I  mean  a  certain  disposition  of  bodies  to  require  more  or  less 
caloric  for  raising  their  temperature  to  any  given  degree  of  heat(4).     Per- 
haps the  fact  may  be  illustrated  thus: 

Let  us  put  as  many  marbles  into  this  glass  as  it  will  contain,  and  pour 
some  sand  over  them;  observe  how  the  sand  penetrates  and  lodges  between 
them.  We  shall  now  fill  another  glass  with  pebbles  o£  various  forms;  you 
see  that  they  arrange  themselves  in  a  more  compact  manner  than  the  mar- 
bles, which,  being  globular,  can  touch  each  other  by  a  single  point  only. 
The  pebbles,  therefore,  will  not  admit  so  much  sand  between  them;  and 
consequently  one  of  these  glasses  will  necessarily  contain  more  sand  than 
the  other,  though  both  of  them  be  equally  full. 

Caroline.  This  I  understand  perfectly.  The  marbles  and  the  pebbles 
represent  two  bodies  of  different  kinds,  and  the  sand  the  caloric  contained 
in  them;  and  it  appears  very  plain,  from  this  comparison,  that  one  body 
may  admit  of  more  caloric  between  its  particles  than  another(S). 

•Mrs  B.  Although  I  have  used  the  pebbles  and  the  marbles  to  enable 
you  the  more  readily  to  lay  hold  of  the  idea,  you  must  not  consider  this  as 
a  satisfactory  explanation  of  the  fact;  for  were  it  so,  the  capacities  of  bodies 
would  diminish  in  the  exact  ratio  of  their  density,  which  is  by  no  means  the 
case;  for,  although,  in  general,  the  most  dense  bodies  have  the  least  capacity, 
this  is  far  from  being  uniformly  the  case.  Oil  occupies  more  space  than 
an  equal  weight  of  water,  and  yet  it  has  but  one  half  the  capacity  for  calo- 
ric; as  that  quantity  which  would  raise  a  pound  of  water  10°  would  produce 
double  that  effect  upon  a  pound  of  oil,  raising  it  20°(6). 

We  are  unacquainted  with  the  cause  of  difference  of  capacity,  and  when- 
ever we  call  to  our  aid  the  operation  of  grosser  matter,  in  illustrating  the 
effects  of  imponderable  agents,  you  must  always  consider  it  as  you  would  a 
figure  in  poetry,  as  bearing  only  an  imaginary  relationship  to  the  fact(7). 

Emily.  But  I  cannot  conceive  why  the  body  that  contains  the  most  calo- 
ric should  not  be  of  the  highest  temperature;  that  is  to  say,  feel  hot  in  pro- 
portion to  the  quantity  of  caloric  it  contains. 

Jlfrs  B.  The  caloric  that  is  employed  in  filling  the  capacity  of  a  body, 
is  not  free  caloric;  but  is  imprisoned,  as  it  were,  in  the  body,  and  is  therefore 
imperceptible:  for  we  can  feel  only  the  caloric  which  the  body  parts  with, 
and  not  that  which  it  retains. 

Caroline.  It  appears  to  me  very  extraordinary,  that  heat  should  be  con- 
fined in  a  body  in  such  a  manner  as  to  be  imperceptible. 

JMrs  B.  If  you  lay  your  hand  on  a  hot  body,  you  feel  only  the  caloric 
•which  leaves  it,  and  enters  your  hand;  for  it  is  impossible  that  you  should  be 
sensible  of  that  which  remains  in  the  body.  The  thermometer,  in  the  same 


3.  What  objection  does  Caroline  make  to  these  examples? 

4.  What  reply  is  given,  and  how  is  this  property  designated? 

5.  By  what  example  is  this  property  illustrated? 

6.  Why  is  not  this  illustration  to  be  considered  as  an  explanation? 

7.  How  are  we  to  consider  such  illustrations? 

* 


COMBINED  CALORIC— SPECIFIC  HEAT.  67 

manner,  is  affected  only  by  the  free  caloric  which  a  substance  transmits  to 
it,  and  not  at  all  by  tbat  which  it  does  not  part  with(8). 

Caroline.  I  begin  to  understand  it;  but  I  confess  that  the  idea  of  insen- 
sible heat  is  so  new  and  strange  to  me,  that  some  time  is  requisite  to  render 
it  familiar. 

•Mrs  B.  Call  it  insensible  caloric,  and  the  difficulty  will  appear  much 
less  formidable.  It  is  indeed  a  sort  of  contradiction  to  call  it  heat,  when  it 
is  so  situated  as  to  be  incapable  of  producing  that  sensation.  Yet  this  modi- 
fication of  caloric  is  commonly  called  SPECIFIC  HEAT(9). 

Caroline.  But  it  certainly  would  have  been  more  correct  to  have  called 
it  specific  caloric. 

Emily.  I  do  not  understand  how  the  term  specific  applies  to  this  modi- 
fication of  caloric. 

Mrs  B.  It  applies  to  the  relative  quantity  of  caloric  which  different 
kinds  or  species  of  bodies,  equal  in  quantity  and  temperature,  are  capable  of 
containing.  The  term,  therefore,  you  must  recollect,  does  not  apply  to  the  heat, 
but  to  the  matter  with  which  it  is  united.  Thus  oil  is  one  species,  or  kind,  of 
matter,  and  water  is  another(lO);  you  have  already  learned  that  they  are 
differently  expanded  by  equal  quantities  of  caloric,  and  you  are  now  to  un- 
derstand that  by  equal  portions  of  it  they  are  also  differently  heated;  this 
arising  undoubtedly  from  the  peculiar  constitution  of  the  bodies,  with  which 
we  do  not  pretend  to  be  acquainted(li). 

Caroline.  Can  you,  Mrs  B.,  show  us  any  of  the  experiments  to  which 
you  have  alluded;  as  the  mere  fact  that  bodies  of  different  kinds  require 
different  periods  of  time  to  bring  them  to  an  equal  degree  of  temperature, 
certainly  cannot  prove  any  thing  more  than  that  they  conduct  heat  in  dif- 
ferent degrees. 

J\frs  B.  The  difficulty  you  urge  would  indeed  be  a  very  serious  one,  if 
we  could  not,  by  reversing  the  experiment,  prove  that  the  milk,  the  chalk, 
and  the  lead,  had  actually  absorbed  different  quantities  of  caloric;  but  this 
we  can  do  by  cooling  the  several  bodies  to  the  same  degree,  in  an  apparatus 
adapted  to  receive  and  measure  the  caloric  which  they  give  out(12).  Thus, 
if  you  plunge  them  into  three  equal  quantities  of  water,  each  at  the  same 
temperature,  you  will  be  able  to  judge  of  the  relative  quantity  of  caloric 
which  the  three  bodies  contained,  by  that  which,  in  cooling,  they  commu- 
nicate to  their  respective  portions  of  water:  for  the  same  quantity  of  calo- 
ric which  they  each  absorbed  to  raise  their  temperature,  will  abandon  them, 
in  lowering  it;  and,  on  examining  the  three  vessels  of  water,  you  will  find 
the  one  in  which  you  immerse  the  lead  to  be  the  least  heated;  that  hi  which 
you  put  the  chalk,  the  next;  and  that  which  contains  the  milk  will  be  heat- 
ed the  most  of  all(13). 

I  have  a  very  convenient  way  of  performing  the  experiment  by  means  of 
these  three  balls  of  metal,  one  of  which  is  copper,  another  tin,  and  the  third 
lead,  each  of  them  weighing-  exactly  eight  ounces.  I  suspend  them  by  a 
thread  in  boiling  water,  and  they  will  all,  consequently,  be  heated  exactly  alike, 
that  is  to  212°.  I  now  suspend  them  in  three  separate  tumblers  of  cold 
water,  a  thermometer  in  each  standing  at  36°.  As  the  water  is  equal  iif 


8.  Why  is  the  heat  of  capacity  insensible? 

9.  What  is  this  modification  of  caloric  called,  and  what  remark  is  made? 

10.  How  is  the  term  specific  heat  applied? 

11.  What  analogous  fact  is  mentioned? 

12.  On  what  principle  can  the  fact  be  shown? 

13.  How  may  this  be  applied? 


68 


CONVERSATIONS  ON  CHEMISTRY. 


quantity  and  temperature,  if  the  three  balls  contain  equal  quantities  of  calo- 
ric, what  will  be  the  effect  upon  the  water? 

Heated  balls  of  Copper,  Lead  and  Tin,  immersed  in  cold  -water 


Copper. 


Lead. 


Tin. 


Emily,     Why  certainly  it  will  be  heated  alike  by  the  metals. 

Mrs  JB.  But  what  will  be  the  result  if  the  metals,  although  of  the  same 
temperature,  contain  unequal  quantities  of  caloric  ? 

Emily.  In  that  case  the  one  having  the  greatest  capacity  will,  of  course, 
in  cooling  down,  heat  the  water  the  most. 

Caroline.  The  difference  is  very  plain.  The  copper  has  raised  the  ther- 
mometer the  most,  the  tin  next,  and  the  lead  least  of  all(l4). 

JMrs  JS.  And  that  is  exactly  the  order  of  their  capacities;  they  being  to 
each  other  as  114,  ,60  and  42.  That  is,  if  the  copper  required  a  quantity  of 
caloric  represented  by  the  number  114  to  elevate  it  a  given  number  of  de- 
grees, the  same  effect  would  be  produced  on  the  tin  by  the  quantity  60,  and 
on  the  lead  by  42(15). 

Emily.  I  think  that  I  have  found  a  comparison  for  specific  heat,  which 
is  very  applicable.  Suppose  that  two  men  of  equal  weight  and  bulk,  but 
who  required  different  quantities  of  food  to  satisfy  their  appetites,  sit  down 
to  dinner,  both  equally  hungry;  the  one  would  consume  a  much  greater 
quantity  of  provisions  than  the  other,  in  order  to  be  equally  satisfied. 

JUrs  B.  Yes,  that  is  very  fair;  for  the  quantity  of  food  necessary  to  sat- 
isfy their  respective  appetites,  varies  in  the  same  manner  as  the  quantity  of 
caloric  requisite  to  raise,  equally,  the  temperature  of  different  bodies(16). 

Emily.  The  thermometer,  then,  affords  no  indication  of  the  specific  heat 
of  bodies. 

JUrs  B.  None  at  all;  no  more  than  satiety  is  a  test  of  the  quantity  of 
food  eaten.  The  thermometer,  as  I  have  repeatedly  said,  can  be  affected 
only  by  free  caloric,  which  alone  raises  the  temperature  of  bodies. 

But  there  is  another  mode  of  proving  the  existence  of  specific  heat,  which 
affords  a  very  satisfactory  illustration  of  the  general  fact.  1  did  not  intro- 
duce it  before,  as  I  thought  it  might  appear  to  you  rather  complicated.  It 
is  this;  if  you  mix  two  fluids,  equal  in  quantity,  but  of  different  temperatures, 
let  us  say  the  one  at  50,  and  the  other  at  100  degrees,  of  what  temperature 
do  you  suppose  the  mixture  will  be? 


14.  What  experiment  is  mentioned,  and  what  its  result? 

15.  What  are  the  order  and  proportion  of  their  capacities? 

16.  By  what  comparison  is  the  nature  of  capacity  illustrated? 


I..  COMBINED  CALORIC—SPECIFIC  HEAT.  69 

Caroline.  It  will  be,  no  doubt,  the  medium  between  the  two,  that  is  to 
say,  75  degrees. 

jfrs  JS.  That  will  be  the  case  if  the  two  bodies  happen  to  have  the  same 
capacity  for  caloric;  but  if  not,  a  different  result  will  be  obtained(17). 
Thus,  for  instance,  if  you  mix  together  equal  weights  of  warm  mercury  and 
cold  water  in  a  jar,  they  are  far  from  producing  a  mean  temperature;  but 
that  of  the  mixture  will  be  much  below  it.  Suppose  the  temperature  of  the 
mercury  to  have  been  156°,  and  the  water  40°;  the  mean  of  these  would 
be  98°,  but  the  resulting  temperature  will  be  only  44°.  Here  then  the  mer- 
cury has"  lost  112°,  whilst  the  water  has  gained  only  4°(18). 

If,  on  the  contrary,  the  water  be  heated  to  156°  and  the  mercury  to  40°,  the 
temperature  of  the  mixture  will  be  152°.  The  water  in  this  case  has  lost 
only  4°;  but  this,  in  entering  into  the  mercury,  has  elevated  it  112°.  In  both 
these  instances  the  capacity  of  water  is  evidently  twenty-eight  times  that  of 
mercury;  or  the  caloric  which  would  elevate  a  pound  of  water  1°  would  ele- 
vate a  pound  of  mercury  28°(19). 

Emily.  But,  Mrs  B.,  it  would  appear  to  me  more  proper  to  compare 
bodies  by  measure,  rather  than  by  -weight,  in  order  to  estimate  their  specific 
heat.  Why,  for  instance,  should  we  not  compare  pints  of  water  and  of  mer- 
cury, rather  than  pounds  of  those  substances;  for  equal  weights  maybe  com- 
posed of  very  different  quantities? 

Mrs  B.  You  are  mistaken,  my  dear;  equal  weights  must  contain  equal 
quantities  of  matter;  and  when  we  wish  to  know  what  is  the  relative  quan- 
tity of  caloric  which  substances  of  various  kinds  are  capable  of  containing 
under  the  same  temperature,  we  must  compare  equal  weights,  and  not  equal 
bulks,  of  those  substances.  .  Bodies  of  the  same  weight  may  undoubtedly  be 
of  very  different  dimensions;  but  this  does  not  change  their  real  quantity  of 
matter(20). 

The  comparison,  however,  has  been  made  in  equal  volumes  as  well  as  in 
equal  weights,  and  the  results  in  either  way  are  equally  various,-  the  gene- 
ral law  may  therefore  be  considered  as  established,  that  different  bodies  in 
equal  quantities,  -whether  estimated  by  weight  or  volume,  contain,  at  any 
given  temperature,  unequal  quantities  of  caloric(21). 

Caroline.  If  all  different  bodies  have  different  capacities  for  caloric,  I 
do  not  see  why  the  same  body  may  not  change  its  capacity  at  different  tem- 
peratures; and,  in  that  case,  the  thermometer  would  not  be  an  accurate 
guide  to  inform  us  of  the  real  quantity  of  caloric  which  left  or  entered  into 
any  substance,  as  this  quantity  would  differ  in  high  and  in  low  tempera- 
tures(22). 

Jtfrs  B.  Very  judiciously  remarked^ndeed.  Much  discussion  has  taken 
place,  and  many  experiments  have  been  made  to  ascertain  this  point;  and 
these  have  resulted  in  proving  that  the  capacities  of  bodies  generally  in- 
crease as  their  temperatures  become  elevated(23).  The  probability  of  this 
had  been  inferred,  from  our  being  able  to  increase  the  temperature  of  a 
body  by  merely  condensing  it,  and  to  decrease  it  by  rendering  it  more  rafre. 
Thus  a  smith  can  take  a  piece  of  cold  iron,  and,  by  hammering  it  smartly, 
heat  it  sufficiently  to  light  a  match,  and  kindle  his  fire.  In  this  case  the 


17.  What  other  mode  is  given,  and  what  remark  is  made  upon  it? 

18.  Give  the  experiment  with  mercury  and  water  at  different  tempera- 
tures. 

19.  What  is  the  result  when  the  experiment  is  reverse 

20.  For  what  reason  are  equal  weights  taken? 

21.  What  is  the  result  with  equal  volumes,  and  what  law  .s  deduced? 

22.  What  remark  does  Caroline  make? 

23.  What  appears  to  be  the  fact  in  this  particular? 


70  CONVERSATIONS  ON  CHEMISTRY. 

*A  \ 

only  change  produced  in  the  iron  is,  that  it  has  heen  condensed  by  closing 
its  pores,  and,  consequently,  a  portion  of  the  heat  which  was  before  latent, 
as  caloric  of  capacity,  has  been  forced  out  and  appears  in  the  form  of  sen- 
sible heat(24). 

Emily,  That  is  both  curious  and  convincing,  and  it  would  follow,  that  if 
•we  could  rarefy  the  iron,  its  capacity  would  be  increased,  and  I  suppose  it 
would  become  colder;  but  how  are  we  to  do  this? 

J\frs  Jf.  We  cannot  mechanically  rarefy  a  solid;  but  by  experimenting 
•with  common  air,  instead  of  with  iron,  I  can  readily  show  you  the  effect  both 
of  rarefaction  arid  condensation.  I  place  a  thermometer  under  the  receiver  of 
the  air  pump,  and  rapidly  exhaust  the  air;  do  you  see  any  change  in  the 
thermometer? 

Emily.  Yes,  it  has  actually  sunk  three  or  four  degrees,  and  appears  to  be 
still  descending(25). 

Mrs  JB.  Now  observe  again;  by  condensing  the  air,  suddenly,  in  this 
brass  tube,  which  you  have  frequently  seen  used,  a  degree  of  heat  will  be 
given  out  sufficient  to  set  fire  to  tinder.  You  therefore  see,  in  the  same 
substance,  the  effect  of  rarefaction  in  increasing,  and  of  condensation  in 
decreasing  capacity(26). 

As  bodies  are  expanded,  and  rendered  more  rare,  by  increase  of  tempe- 
rature, the  inference  seems  natural  that  as  they  become  expanded  their  ca- 
pacities should  also  increase;  and  under  these  circumstances,  if  caloric  be 
communicated  to  them,  one  portion  of  it  goes  to  satisfy  this  increased  capa- 
city, whilst  another  serves  to  elevate  the  temperature(27).  But  let  us  now 
proceed  to  LATENT  HEAT. 

Caroline.  And  pray  what  kind  of  heat  is  that?  I  had  thought  that  heat 
of  capacity  was  sufficiently  latent,  as  it  is  completely  hidden  in  a  body,  pro- 
ducing no  apparent  effect  upon  it.  How,  I  wonder,  can  any  thing  be  more 
latent  than  this? 

Mrs  B.  The  heat  of  which  I  speak  is  another  modification  of  combined 
calorie,  which  is  so  analogous  to  specific  heat,  thai  many  chemists  think  it 
unnecessary  to  make  any  distinction  between  them;  but  the  term  specific 
heat  is  generally  confined  to  that  portion  which  goes  to  satisfy  the  capacity  of 
a  body,  whilst  its  form  remains  unchanged,  and  we  denominate  latent  heat 
that  portion  of  caloric  which  is  employed  in  changing  the  state  of  bodies, 
that  is  to  say,  in  converting  solids  into  liquids,  or  liquids  into  vapour(28). 
When  a  body  changes  its  form  from  solid  to  liquid,  or  from  liquid  to  va- 
pour, a  sudden  and  considerable  increase  of  capacity  for  heat  uniformly  ac- 
companies the  change,  and  in  consequence  of  this  it  immediately  absorbs  a 
quantity  of  caloric,  which  becomes  fixed  in  the  body  it  has  transformed;  and 
as  it  is  perfectly  concealed  from  our  senses,  it  has  obtained  the  name  of 


Caroline.  I  think  it  would  be  much  more  correct  to  call  this  modifica- 
tion latent  caloric  than  latent  heat,  since  it  does  not  excite  the  sensation 
of  heat. 

J\frs  B.  It  was  discovered  and  named  by  Dr  Black  long  before  the 
French  chemists  introduced  the  term  caloric,  and  we  must  not  presume  to 
change  the  name,  as  it  is  still  used  by  much  better  chemists  than  ourselves. 
Besides,  you  are  not  to  suppose  that  the  nature  of  heat  is  altered  by  being 


24.  What  effect  is  produced  by  hammering  iron,  &c.  ? 

25.  How  may  the  effect  of  rarefaction  be  shown  by  the  air  pump? 

26.  What  effect  may  be  produced  by  condensing  air? 

27.  What  inference  may  be  drawn  from  these  facts? 

28.  What  distinction  is  made  between  specific  and  latent  heat? 

29.  Under  what  circumstances  does  heat  become  latent? 

u 


COMBINED  CALORIC—LATENT  HEAT.  71 

variously  modified:  for  if  latent  heat  and  specific  heat  do  not  excite  the  same 
sensation  as  free  caloric,  it  is  owing  to  their  being  in  a  state  of  confinement, 
which  prevents  them  from  acting  upon  our  organs;  and,  consequently,  as 
soon  as  they  are  extricated  from  the  body  in  which  they  are  imprisoned, 
they  return  to  their  state  of  free  caloric(SO). 

Emily.  But  I  do  not  yet  clearly  see  i  n  what  respect  latent  heat  differs  from 
specific  heat;  for  they  are  both  of  them  imprisoned  and  concealed  in  bodies, 

»Mrs  JB.  Specific  heat  is  that  which  is  employed  in  filling  the  capacity 
of  a  body  for  caloric,  in  the  state  in  which  this  body  actually  exists;  while 
latent  heat  is  that  which  is  employed  only  in  effecting  a  change  of  state,  that 
is,  in  converting  bodies  from  a  solid  to  a  liquid,  or  from  a  liquid  to  an  aeri- 
form state.  But  I  think,  that  in  a  general  point  of  view,  both  these  modi- 
fications might  be  comprehended  under  the  name  of  heat  of  capacity,  as  in 
both  cases  the  caloric  is  equally  engaged  in  filling  the  capacity  of  bodies(31). 

I  shall  now  show  you  an  experiment,  which  I  hope  will  give  you  a  clear 
idea  of  what  is  understood  by  latent  heat. 

The  ice  which  you  see  in  this  phial  has  been  cooled  by  certain  chemi- 
cal means,  (which  I  cannot  well  explain  to  you  at  present,)  to  five  or  six 
degrees  below  the  freezing  point,  as  you  will  find  indicated  by  the  thermo- 
meter which  is  placed  in  it.  We  will  expose  it  to  the  heat  of  the  fire,  and 
you  will  see  the  thermometer  gradually  rise,  till  it  reaches  the  freezing 
point 

Emily.  But  there  it  stops,  Mrs  B.,  and  yet  the  fire  burns  just  as  well 
as  before.  Why  is  not  its  heat  cpmmunicated  to  the  thermometer? 

Caroline.  And  the  ice  begins  to  melt;  therefore  it  must  be  rising 
above  the  freezing  point. 

Jlfrs  JB.  The  heat  no  longer  affects  the  thermometer,  because  it  is 
wholly  employed  in  converting  the  ice  into  water.  As  the  ice  melts,  the 
caloric  becomes  latent  in  the  new  formed  liquid,  and  therefore  cannot  raise 
its  temperature;  and  the  thermometer  will  consequently  remain  stationary, 
until  the  whole  of  the  ice  be  melted(32). 

Caroline.     Now  it  is  all  melted,  and  the  thermometer  begins  to  rise  again. 

Mrs  B.  Because  the  conversion  of  the  ice  into  water  being  completed, 
the  caloric  no  longer  becomes  latent;  and  therefore  the  heat  which  the  water 
now  receives  raises  its  temperature,  as  you  find  indicated  by  the  thermome- 
ter(33). 

Emily.  But  I  do  not  think  that  the  thermometer  rises  so  quickly  in  the 
water  as  it  did  in  the  ice,  previously  to  its  beginning  to  melt,  though  the 
fire  burns  equally  well.  ^ 

Mrs  JB.  That  is  owing  to  the  different  specific  heat  of  ice  and  water. 
The  capacity  of  water  for  caloric  being  greater  than  that  of  ice,  more  heat 
is  required  to  raise  its  temperature,  and  therefore  the  thermometer  rises 
slower  in  the  water  than  it  did  in  the  ice(34). 

Emily.  True;  you  said  that  a  solid  body  always  increased  its  capacity 
for  heat  by  becoming  fluid,  and  this  is  an  instance  of  it. 

J\frs  J3.  Yes;  and  the  latent  heat  is  that  which  is  absorbed  in  conse- 
quence of  the  increased  capacity  resulting  from  the  change  of  form.  This 
increased  capacity  in  the  water  is  not  the  result  of  expansion,  but  merely  of 
the  change  to  the  liquid  state,  for  the  water  is  in  fact  more  dense  than  the 


SO.  Who  discovered  latent  heat,  and  what  is  remarked  respecting  it? 

31.  What  further  is  said  of  the  distinction  between  specific  and  latent 
heat? 

82.  What  experiment  is  detailed  showing  the  absorption  of  heat? 

33.  What  occurs  after  the  snow  has  melted,  and  why? 

34.  Why  did  the  thermometer  rise  most  rapidly  in  the  snow? 


T2  CONVERSATIONS  ON  CHEMISTRY. 

ice,  as  you  may  know  by  the  floating  of  ice  upon  water(35).  You  have  al- 
ready learned  that  in  rendering  a  substance  liquid,  the  caloric  is  employed 
in  modifying  the  attraction  of  the  particles  so  as  to  produce  the  fluid  form; 
and  whilst  so  employed  it  evidently  must  be  latent,  for  if  it  could  puss  into 
your  hand,  or  into  any  thing  else,  in  the  form  of  free  caloric,  it  must,  in  that 
case,  leave  the  water,  and  this  would  be  brought  back  to  the  state  of  ice(36). 
The  caloric  employed  in  rendering  bodies  liquid  is  frequently  called  the 
caloric  offluidity(37). 

Caroline.  Have  you  any  means  of  ascertaining  the  quantity  of  heat  which 
is  rendered  latent  in  the  conversion  of  ice  into  water;  for  it  would  seem, 
from  the  length  of  time  required  to  melt  the  ice  before  the  fire,  that  it  must 
be  very  considerable? 

JHrs  Ji.  We  can  fortunately  do  this  at  once,  as  there  is  now  dry  snow  upon 
the  ground.  I  have  ordered  a  pound  of  it  to  be  weighed,  and  put  into  a 
wooden  bowl,  and  you  see  that  a  thermometer,  placed  in  it,  stands  at  32°. 
In  this  cup  I  have  a  pound  of  water  which  is  heated,  as  you  perceive,  to 
172°,  or  within  40°  of  boiling.  This  I  pour  upon  the  snow,  and  stir  it  about; 
now  you  see  the  snow  has  thawed. 

Emily.  Yes!  and  what  is  most  surprising,  the  thermometer  in  the  bowl 
still  stands  at  32°.  I  had  been  calculating  that  the  mean  was  102°  and  al- 
though 1  expected  to  see  it  below  this,  I  never  should  have  believed  that  all 
the  heat  would  be  lpst(38). 

Caroline.  The  pound  of  hot  water  has  actually  lost  140°  of  heat,  and  the 
whole  of  this  must  have  become  latent  in  converting  the  same  weight  of  ice 
into  the  fluid  form.  What  an  enormous  quantity  of  heat  there  must  be  in  the 
water  of  the  ocean!  If  it  could  at  once  become  sensible  heat,  the  water 
would  all  be  ready  to  boil(39). 

Emily.  What  would  have  been  the  effect  if  the  water  in  the  cup  had 
been  heated  to  176°  instead  of  172°.  Would  the  temperature  of  the  mix- 
ture then  have  been  32°  ? 

JWrs  B.  By  no  means:  140°  would  still  have  disappeared,  and  the  4° 
of -excess  would  have  been  diffused  throughout  the  two  pounds  of  water,  so 
that  the  thermometer  would  have  stood  at  34°(40). 

We  might  perform  many  other  experiments  in  confirmation  of  the  fact 
just  explained;  but  we  have  much  to  do,  and  one  or  two  convincing  and 
unexceptionable  proofs  are  sufficient  for  our  purpose;  and  indeed  a  greater 
number  would  be  more  likely  to  confuse  than  to  instruct  you.  During 
our  progress  you  will  witness  many  experiments,  which,  whilst  they  are  in- 
troduced to  prove  other  points,  will  furnish  additional  evidence  of  the  truth 
of  that  which  I  have  just  explained  to  you. 

You  have  observed  me  place  this  flask,  half  filled  with  water,  over  the 
lamp.  Within  it  are  two  thermometers,  the  bulb  of  one  immersed  in  the 
liquid,  whilst  the  other  is  suspended  above  it.  The  water  is  near  boiling, 
and  I  wish  you  to  notice  what  takes  place  *s  it  becomes  converted  into 
vapour. 


85.  Does  not  the  increased  capacity  result  from  expansion? 

36.  What  reason  is  given  why  the  caloric  must  be  latent? 

37.  What  other  name  is  given  to  this  modification  of  heat? 

38.  How  may  the  loss  of  heat  in  melting  ice  be  shown? 

39.  What  quantity  becomes  latent,  and  how  is  this  proved? 

40.  If  the  water  had  been  heated  to  176°,  what  would  have  been  the  re- 
*lt> 


COMBINED  CALORIC—LATENT  HEAT. 


73 


Caroline.  The  thermometer  placed  within  the  water  is  rising;  it  is  now 
212°  and  the  water  begins  to  boil,  but  the  thermometer  remains  stationary, 
although  heat  must  still  be  flowing  in  as  rapidly  as  before;  this  is  wonderfully 
curious !  The  caloric  must  now  be  busy  in  changing  the  water  into  steam, 
in  which  it  hides  itself,  and  becomes  insensible.  This  is  another  example 
of  latent  heat  producing  a  change  of  form.  At  first  it  converted  a  solid 
body  into  a  liquid,  and  now  it  turns  the  liquid  into  vapour. 

Mrs  B.  If  you  observe  the  thermometer  which  is  placed  above  the 
liquid,  and  surrounded  by  the  steam,  you  will  see  that  it  also  stands  at  212°; 
yet  you  will  soon  learn  that  the  steam  has  absorbed  a  vast  deal  more  heat 
than  the  ice  did  in  thawing(41).  If  we  were  now  to  reverse  these  changes, 
and  condense  the  vapour  into  water,  and  the  water  into  ice,  all  the  latent 
heat  would  reappear  in  the  form  of  free  caloric(42). 


Fig.  1. 


Fig.  2. 


[Fig.  1.   Apparatus  showing  that  boiling  water  and  steam  are  equal  in  tempe- 
rature.    Fig.  2.  Steam  from  boiling,  condensed  by  cold  water.  ] 

Emily.     Pray  do  let  us  see  the  effect  of  latent  heat  returning  to  its  free  state. 

Mrs  B.  For  the  purpose  of  showing  this,  we  need  simply  conduct  the 
vapour  through  the  tube  into  this  vessel  of  cold  water,  where  it  will  part 
with  its  latent  heat  and  return  to  its  liquid  form(43). 

Emily.     How  rapidly  the  steam  heats  the  water! 

Mrs  B.  That  is  because  it  does  not  impart  to  it  its  free  caloric  merely, 
but  likewise  its  latent  heat;  and  so  great  is  the  amount  thus  communicated, 
that  when  the  water  in  the  jar  has  had  one  ounce  added  to  it  by  the 
condensation  of  the  steam,  this  steam  will  have  elevated  its  temperature 
about  seven  times  as  much  as  an  ounce  of  boiling  water  would  have  done; 
and  hence  it  results  that  an  ounce  of  steam  at  212°,  contains  seventimes  as 


41.  Detail  the  experiment  of  boiling  water  in  a  flask,  with  the  result. 

42.  What  is  it  said  would  result  from  reversing  the  experiment? 

43.  How  may  this  be  effected? 

G 


74  CONVERSATIONS  ON  CHEMISTRY. 

much  caloric  as  an  ounce  of  water  at  the  same  temperature(44).  By  an 
easy  calculation,  therefore,  it  can  be  shown  that  steam  contains  a  quantity 
of  caloric  in  a  latent  state,  which,  if  it  could  be  confined  within  it,  would, 
in  the  form  of  free  heat,  elevate  its  temperature  to  950°;  a  portion  more  than 
sufficient  to  render  it  red  hot(45).  You  may  readily  judge,  therefore,  why 
steam,  issuing  from  boiling  water,  should  scald  so  severely,  although  its 
quantity  maybe  very  small.  When  it  comes  into  contact  with  the  body,  this 
being  cooler,  condenses  it,  and  the  steam  gives  out  its  latent  heat(46). 

Caroline.  In  natural  evaporation,  at  common  temperatures,  the  water 
which  exists  in  the  atmosphere  in  the  form  of  vapour,  must  pass  into  that 
state  without  combining  with  such  an  enormous  quantity  of  caloric. 

Mrs  B.  On  the  contrary,  it  has  been  found  that  vapour  at  low  tempera- 
tures contains  more  latent  heat  than  that  at  212°,  its  latent  heat  being  increas- 
ed in  proportion  as  its  sensible  heat  is  diminished;  so  that  if  the  tempera- 
ture were  150°  below  the  boiling  point,  the  latent  heat,  instead  of  being 
950°,  would  be  1100°(47). 

We  cannot  perform  the  experiments  which  demonstrate  this  fact,  but  the 
proofs  of  it  are  quite  satisfactory;  and  the  importance  of  that  law  in  the 
economy  of  nature,  with  its  results,  will,  by  and  bye,  be  pointed  out  to  you. 
Emily.  We  have  seen  the  latent  heat  of  steam  set  free  by  the  return  of 
the  steam  to  the  liquid  state.  I  should  like  also  to  see  that  of  water  given 
out  on  its  conversion  into  ice. 

Caroline.  That  must  not  only  be  difficult,  but,  I  should  suppose,  impos- 
sible in  this  warm  room. 

Jlfrs  B.  So  far  from  being  impossible,  it  is  by  no  means  difficult.  To 
freeze  milk,  requires  a  temperature  somewhat  below  that  for  water;  yet  ice 
cream  is  made  abundantly  in  summer.  I  believe,  Caroline,  vou  know  the 
manner  in  which  this  is  effected? 

Caroline.  Yes;  the  teilk,  or  cream,  to  be  frozen,  is  put  into  a  metallic 
vessel,  and  this  is  placed  within  another  vessel  of  wood,  and  surrounded  by  a 
mixture  of  ice  and  common  salt,  which  produces  a  degree  of  cold  sufficient 
to  freeze  the  cream(48).  I  have  often  assisted  in  making  it,  but  have  never 
been  able  to  understand  why  the  mixing  of  salt,  which  itself  is  not  cold, 
should  produce  a  more  intense  cold  than  that  of  the  ice  alone,  and  particu- 
larly, as  I  have  always  observed  that  the  salt  causes  the  ice  to  melt,  and 
must  therefore  communicate  heat  to  it(49). 

J\frs  B.  What  you  have  just  learned  will  enable  you  to  solve  the  mys- 
tery. We  will  now  mix  some  snow  and  salt  in  this  tin  cup;  you  see  that 
they  immediately  begin  to  melt,  and  that  the  moisture  of  the  atmosphere 
condenses  on  the  outside,  and  forms  a  coat  of  ice(50). 

Emily.  The  mixture  feels  much  colder  than  the  ice  itself,  and  yet  it  is 
becoming  liquid.* 

J\frs  B.  It  is  that  very  circumstance  which  causes  the  intense  cold;  and 
it  was  by  this  same  means  that  Fahrenheit-  obtained  the  zero  of  his  scale. 
You  see  that  a  thermometer  placed  in  it  sinks  upwards  of  32°  below  freez- 
ing, or  to  zero,  represented  by  a  0°. 

The  cause  of  the  intense  cold  of  the  mixture,  is  that  change  from  the  solid 
to  the  fluid  state,  by  which  its  capacity  for  caloric  is  so  greatly  increased; 


44.  What  is  the  heat  in  steam  compared  with  that  in  boiling  water? 

45.  What  is  proved  respecting  the  quantity  of  heat  latent  in  steam? 

46.  Why  does  steam  scald  more  violently  than  boiling  water? 

47.  WThat  is  the  fact  respecting  the  latent  heat  of  atmospheric  vapour? 

48.  What  is  the  process  for  making  ice  cream? 

49.  What  puzzling  circumstance  does  Caroline  mention? 

50.  What  is  the  effect  of  mixing  snow  and  salt? 


COMBINED  CALORIC— LATENT  HEAT.  75 

and  of  course,  to  satisfy  this  increased  capacity,  it  must  absorb  caloric  from 
the  surrounding  bodies,  and  consequently  produce  cold  in  them(51). 

Caroline.  I  must  have  been  stupid  not  to  recollect  that,  as  it  follows  of 
necessity  from  the  doctrine  of  latent  heat;  but  still  I  do  not  see  why  it 
should  not  itself  freeze,  as  it  is  colder  than  ice,  nor  what  can  have  become 
of  the  32°  which  it  has  lost. 

Mrs  B.  I  am  apprehensive  that  you  will  again  lay  claim  to  the  crown 
of  stupidity,  however  willing  you  may  be  to  have  your  title  disputed.  If 
caloric  be  rendered  latent  when  a  body  changes  its  form,  it  must  first  have 
been  free.  When  the  salt  and  snow  melt,  a  portion  of  their  own  free  caloric 
is  converted  into  caloric  of  fluidity;  but  this  being  insufficient  to  satisfy  the 
increased  capacity,  an  additional  portion  is  taken  from  the  bodies  in  contact 
with  the  mixture,  and  thus  their  temperature  is  also  lowered(52). 

If  we  mix  salt  with  water,  the  brine  which  we  produce  will  not  freeze 
until  it  is  cooled  some  degrees  below  the  freezing  point  of  fresh  water;  the 
number  of  degrees  depending  upon  the  quantity  of  salt  which  has  been  dis- 
solved. Sea-water  therefore  requires  a  more  intense  cold  to  freeze  it  than 
river  water.  When  water  is  saturated  with  salt,  its  freezing  ponSt  is  lowered 
at  least  32°,  or  down  to  0°;  and  hence,  whilst  its  temperature  is  above  zero, 
it  must  remain  fluid(53). 

Emily.      Whatever  you  put  in  this  mixture,  then,  would  freeze? 

Mrs  B.  Not  every  liquid,  but  any  one  that  is  susceptible  of  freezing  at 
that  temperature.  I  have  prepared  another  mixture  of 
salt  and  snow,  for  the  purpose  of  freezing  the  water  from 
which  you  are  desirous  of  seeing  the  latent  heat  escape. 
The  snow  and  salt  are  in  this  tin  cup,  and  I  immerse  in  it  a 
smaller  vessel  containing  the  water  to  be  frozen.  I  have 
put  a  thermometer  in  the  water,  in  order  that  you  may 
observe  its  rate  of  cooling. 

Caroline.     The  thermometer  descends,  but  the  heat 
which  the  water  is  now  losing  is  its  free,  not  its  latent     LTm  CUP  contam- 
neat.  ing  snow  and  salt, 

Mrs  B.  Certainly;  it  does  not  part  with  its  latent  the  i.nner,  vessel 
heat  till  it  changes  its  state  and  is  converted  into  ice.  containing  water 

Emily.     But  here  is   a  very   extraordinary  circum-     to  be  frozen.] 
stance!     The  thermometer  has  fallen  below  the  freezing 
point,  and  yet  the  water  is  not  frozen. 

Mrs  B.  Such  is  always  the  case  previously  to  the  freezing  of  water, 
when  it  is  in  a  state  of  perfect  rest.  Now  it  begins  to  congeal,  and  you 
may  observe  that  the  thermometer  again  rises  to  the  freezing  point(54). 

Caroline.  It  appears  to  me  very  strange  that  the  thermometer  should 
rise  the  very  moment  that  the  water  freezes;  for  it  seems  to  imply  that  the 
water  was  colder  before  it  froze  than  when  in  the  act  of  freezing. 

Mrs  B.  So  it  was;  and  after  our  long  dissertation  on  this  circumstance, 
I  did  not  think  it  would  appear  so  surprising  to  you.  Reflect  a  little,  and  I 
think  you  will  discover  the  reason  of  it. 

Caroline.  It  must  be,  no  doubt,  the  extrication  of  latent  heat,  at  the  in- 
stant the  water  freezes,  which  raises  the  temperature. 

Mrs  B.  Certainly:  and  if  you  now  examine  the  thermometer,  you  will 
find  that  its  rise  was  but  temporary,  and  lasted  only  during  the  disengage- 


51.  What  is  the  explanation? 

52.  What  becomes  of  the  caloric  apparently  lost? 

53.  What  prevents  the  mixture  from  freezing  at  so  low  a  temperature? 

54.  Detail  the  phenomena  attending  the  freezing  of  water  by  snow  and 
salt. 


76  CONVERSATIONS  ON  CHEMISTRY. 

raent  of  the  latent  heat.  Now  that  all  the  water  is  frozen,  it  again  falls,  and 
will  continue  to  fall  till  the  ice  and  mixture  are  of  an  equal  tempera- 
ture^ 5). 

As  there  is  some  intricacy  in  this  subject,  I  must  not  hurry  you  on  too 
far.  We  will  therefore  dismiss  it  until  to-morrow;  and  I  can  assure  you  that 
if  you  preserve  a  distinct  recollection  of  the  facts  and  explanations  which 
have  occupied  us  to-day,  you  will  deserve  no  small  praise. 


CONVERSATION  VII. 

LATENT  HEAT  CONTINUED. 

Heat  rendered  sensible  by  Solidification.  Freezing1  by  Evaporation  and  by 
Mixture.  Natural  Temperature,  how  equalized.  J)ew.  Hoar  Frost. 
Clouds.  Fogs.  Rain.  Snow.  Hail.  Causes  of  Cold  at  great  Heights. 

Emily.  I  have  been  thinking,  Mrs  B.,  that  if  there  were  any  liquids 
•which  would  become  solid  by  merely  mixing  them,  their  latent  heat  would 
be  suddenly  disengaged;  are  there  any  such? 

Mrs  B.  I  could  show  you  several,  and  although  you  are  not  sufficiently 
far  advanced  to  understand  perfectly  all  the  attending  circumstances,  1  will 
exhibit  to  you  one  which  will  afford  a  striking  example  of  the  fact. 

The  fluid  which  you  see  in  this  phial  is  a  solution  in  water  of  a  certain 
salt  called  muriate  of  lime.  In  this  other  phial  I  have  a  saturated  solution 
of  sulphate  of  soda,  (common  Glauber's  salt).  On  mixing  and  stirring  them 
together,  the  whole,  or  very  nearly  the  whole,  will  be  rapidly  converted 
into  a  solid  mass(l). 

Emily.  How  white  it  turns!  I  feel  it  quite  warm,  from  the  escape  of 
the  heat  that  was  latent  in  the  fluids,  which  have  now  changed  into  a  solid 
substance  like  chalk.  This  is  really  one  of  the  most  curious  experiments 
we  have  yet  seen;  it  seems  quite  a  miracle. 

Mrs  B.  It  is  sometimes  called  the  chemical  miracle;  and  I  think  that 
even  to  the  chemist,  who  is  familiar  with  its  cause,  it  must  always  appear 
highly  interesting(2). 

I  will  show  you  another  instance  similar  to  that  of  the  water,  which  you 
observed  to  become  warmer  as  it  froze.  I  have  in  this  flask  a  solution  of 
sulphate  of  soda,  (Glauber's  salt,)  made  very  strong;  it  was  corked  up 
•whilst  boiling  hot,  and  kept  without  agitation  till  it  became  cold,  as  you 
may  feel  it  now  is.  When  I  take  out  the  cork  and  allow  the  atmosphere  to 
press  upon  it,  (for  being  closed  when  boiling,  there  is  a  vacuum  in  the 
upper  part,)  observe  that  the  salt  will  suddenly  crystallize. 

Caroline.  Surprising!  how  beautifully  the  needles  of  salt  have  shot 
through  the  whole  flask ! 

Mrs  B.  The  experiment  succeeds  sometimes,  although  the  flask  be  not 
closely  stopped,  provided  the  solution  be  kept  from  all  agitation.  When 
the  crystallization  does  not  readily  take  place,  a  small  piece  of  the  solid 
salt  dropped  in  will  instantaneously  produce  it.  But  let  us  not  forget  the 
object  of  the  experiment.  Feel  how  warm  the  flask  has  become  by  the  con- 
version of  a  part  of  the  liquid  into  a  solid. 


55.  What  are  the  causes  of  the  rise  and  fall  of  temperature  ? 

1.  What  two  solutions  become  solid  by  mixture? 

2.  What  law  does  this  exemplify,  and  what  is  the  phenomenon  called? 


LATENT  HEAT  CONTINUED.  7jr 

Emily.  Quite  warm,  I  declare!  This  is  a  most  curious  exemplification 
of  the  disengagement  of  latent  heat(3). 

Mrs  B.  The  slaking  of  lime  affords  another  remarkable  instance  of  the 
conversion  of  latent  into  sensible  heat.  Have  you  never  observed  how  quick- 
lime smokes  when  water  is  poured  upon  it,  and  how  much  heat  it  produces? 

Caroline.  Yes;  but  I  do  not  understand  what  change  of  state  takes  place 
in  the  lime  that  occasions  its  giving  out  latent  heat;  for  the  quick-lime, 
which  is  solid,  is  reduced  to  powder  by  the  operation  of  slaking,  and  is, 
therefore,  rather  expanded  than  condensed. 

Mrs  B.  It  is  from  the  water,  not  from  the  lime,  that  the  latent  heat  is  set 
free.  The  water  combines  with,  and  becomes  solid  in  the  lime;  in  conse- 
quence of  which  chemical  union,  the  heat,  which  kept  it  in  a  liquid  state,  is 
disengaged,  and  escapes  in  a  sensible  form(4). 

Caroline.  I  always  thought  that  the  heat  originated  in  the  lime.  It  seems 
very  strange  that  water,  and  cold  water  too,  should  contain  so  much  heat. 

Emily.  Then  after  this  extrication  of  caloric,  the  water  must  exist  in  the 
lime  in  the  state  of  ice,  since  it  parts  with  the  heat  which  kept  it  liquid. 

Mrs  B.  It  cannot  properly  be  called  ice,  since  ice  implies  a  degree 
of  cold,  at  least  equal  to  the  freezing  point.  Yet,  as  water,  in  combining 
with  lime,  gives  out  more  heat  than  it  does  in  freezing,  it  must  be  in  a  state 
of  still  greater  solidity  in  the  lime  than  when  in  the  form  of  ice;  and  you 
may  have  observed  that  it  does  not  moisten  or  liquefy  the  lime  in  the 
smallest  degree(5).  Quick-lime  converts  into  the  solid  state  about  a  third 
of  its  own  weight  of  water.  If  more  than  this  be  added,  the  excess  will  re- 
main in  the  liquid  state,  and  moisten  the  lime.  The  former  portion  is  che- 
mically combined,  the  latter  merely  mixed(6).  « 

Emily.  But,  Mrs  B.,  the  smoke  that  rises  is  white:  if  it  was  only  pure 
calorie  which  escaped,  we  might  feel,  but  could  not  see  it. 

Mrs  B.  This  white  vapour  is  formed  by  some  of  the  particles  of  lime, 
in  a  state  of  fine  dust,  which  are  carried  off  by  the  caloric,  united  with  a 
portion  of  water  evaporated  by  the  heat(7). 

Emily.  In  all  changes  of  form,  then,  a  body  either  absorbs  or  disengages 
latent  heat? 

Mrs  B.  You  cannot  exactly  say  absorbs  latent  heat,  as  the  heat  becomes 
latent  only  on  being  confined  in  the  body;  but  you  may  say,  generally,  that 
bodies  in  passing  from  a  solid  to  a  liquid  form,  or  from  the  liquid  form  to  that 
of  vapour,  absorb  heat;  and  that  -when  the  reverse  changes  take  place,  heat 
is  disengaged.  To  this  law  there  are,  it  is  true,  some  exceptions,  which 
will  be  hereafter  noticed(S). 

Emily.  We  can  now,  I  think,  account  for  the  ether  boiling,  and  the  wa- 
ter freezing  in  vacuo,  at  the  same  temperature. 

Mrs  B.     Let  me  hear  how  you  explain  it. 

Emily.  The  latent  heat  which  the  water  gave  out  in  freezing,  was  im- 
mediately absorbed  by  the  ether,  during  its  conversion  into  vapour;  and, 
therefore,  from  a  latent  state  in  the  water,  it  passed  into  a  latent  state  in  the 
vapour  of  the  ether. 

Mrs  B.  You  are  so  far  correct;  but  it  remains  to  be  explained  why  the 
temperature  of  the  ether  is,  by  its  own  ebullition,  brought  down  to  the 
freezing  temperature  of  water.  It  is  because  that  part  of  the  ether  which  is 


3.  What  analogous  experiment  is  given  with  sulphate  of  soda? 

4.  Whence  is  heat  derived  in  slaking  lime? 

5.  In  what  state  does  the  combined  water  exist? 

C.  In  what  proportion  is  it  rendered  solid  by  the  lime? 

7.  Of  what  does  the  white  vapour  which  escapes  consist? 

8.  What  general  law  is  given,  and  is  it  universal  ? 

G  2 


78  CONVERSATIONS  ON  CHEMISTRY. 

evaporated,  must  rob  that  portion  which  remains  liquid  of  its  free  caloric, 
which  it  converts  into  a  latent  state.  This  cooled  ether  must  cool  the  wa- 
ter; so  that  though  one  liquid  boils,  and  the  other  freezes,  their  tempera- 
tures are  equally  reduced(9). 

Emily.  But  why  does  not  water,  as  well  as  ether,  reduce  its  own  tem- 
perature by  evaporating? 

J\frs  B.  It  does  so,  in  fact,  though  much  less  rapidly  than  ether.  Thus, 
for  instance,  you  may  often  have  observed,  in  the  heat  of  summer,  how  much 
any  particular  spot  may  be  cooled  by  sprinkling  it  with  water,  although  the 
water  used  may  be  as  warm  as  the  air  itself(lO).  Indeed  so  much  cold  may 
be  produced  by  the  mere  evaporation  of  water,  that  the  inhabitants  of  India 
succeed  in  causing  it  to  freeze,  though  the  temperature  of  the  air  be  as  high 
as  40  degrees.  This  they  do  by  availing  themselves  of  the  most  favourable 
circumstances  for  the  process,  which  their  warm  climate  and  dry  atmosphere 
can  afford,  namely,  the  coolness  of  night,  and  situations  most  exposed  to  its 
drying  breezes.  The  water  is  put  into  shallow  earthen  trays,  so  as  to  ex- 
pose an  extensive  surface  to  the  process  of  evaporation,  and  in  the  morning, 
the  water  is  found  covered  with  a  thin  cake  of  ice,  which  is  collected  in  suf- 
ficient quantity  to  be  used  for  purposes  of  luxury(ll). 

Caroline.  How  delicious  it  must  be  to  drink  liquids  so  cold  in  those 
tropical  climates!  But,  Mrs  B.,  could  we  not  try  that  experiment? 

Mrs  B.  Much,  in  this  case,  depends  upon  the  rapidity  of  the  evapora- 
tion, and  this  is  materially  influenced  by  the  state  of  the  atmosphere,  which 
in  our  climate  generally  contains  too  much  moisture  to  allow  us  to  hope  for 
success  in  such  a  trial(12).  We  are  not,  however,  entirely  without  analogous 
facts.  It  has  been  often  observed  that  wet  clothes  have  frozen  when  hung 
out  to  dry,  although  the  temperature  of  the  air  has  been  three  or  four  de- 
grees above  freezing;  the  rapidity  of  the  evaporation  at  the  time  of  a 
brisk  breeze  and  a  dry  atmosphere,  being  sufficient  to  produce  the  effect(13). 

We  can,  upon  a  small  scale,  freeze  water  by  its  own  evaporation  in  this 
very  room,  in  which  the  thermometer  stands  at  70  degrees.  For  this  pur- 
pose we  must  place  some  water  in  a  shallow  dish  under  the  receiver  of  the 
air  pump,  and  exhaust  the  air  from  it.  What  will  be  the  consequence, 
Caroline  ? 

Caroline.  Of  course  the  water  will  evaporate  more  quickly,  since  there 
will  no  longer  be  any  atmospheric  pressure  on  its  surface;  but  will  this  be 
sufficient  to  make  the  water  freeze  ? 

Mrs  B.  No,  because  the  vapour  will  not  be  carried  off  fast  enough; 
but  this  will  be  accomplished,  without  difficulty,  if  we  introduce  into  the  re- 
ceiver, in  a  large  shallow  vessel,  some  strong  sulphuric  acid,  (oil  of  vitriol,) 
a  substance  which  has  a  great  attraction  for  water,  whether  in  the  form  of 
vapour  or  in  the  liquid  state.  This  attraction  is  such  that  the  acid  will  in- 
stantly absorb  the  moisture  as  it  rises  from  the  water,  so  as  to  make  room 
for  the  formation  of  fresh  vapour.  This  will  of  course  hasten  the  process, 
and  the  cold  produced  from  the  rapid  evaporation  of  the  water,  will  in  a 
few  minutes  be  sufficient  to  freeze  its  surface.  We  shall  now  exhaust  the 
air  from  the  receiver(l4). 


9.   Can  you  give  the  rationale  of  the  freezing  of  water  by  boiling  ether? 

10.  What  is  remarked  concerning  the  evaporation  of  water? 

11.  What  is  mentioned  relating  to  the  production  of  ice  in  India? 

12.  Why  may  not  this  be  effected  every  where? 

13.  What  circumstance  occurs  in  our  own  climate   dependent  on  this 
same  principle? 

14.  How  are  we  enabled  to  freeze  water  by  its  own  evaporation? 


LATENT  HEAT  CONTINUED, 


79 


Ji-'imiimmniiM. 

[Plate  of  the  air  pump  covered  with  a  large  receiver,  under  which  is  a  glass 
vessel  containing  sulphuric  acid,  with  a  thin  cup  suspended  above  it,  in 
•which  there  is  a  portion  of  water  to  be  frozen  by  its  own  evaporation.] 

Emily.  Thousands  of  small  bubbles  already  rise  through  the  water  from 
the  internal  surface  of  the  cup;  what  is  the  reason  of  this? 

•Mrs  B.  These  are  bubbles  of  air  which  were  partly  attached  to  the  vessel, 
and  partly  diffused  in  the  water  itself;  and  they  expand  and  rise  in  conse- 
quence of  the  atmospheric  pressure  being  removed(15). 

Caroline.  See,  Emily,  the  thermometer  in  the  cup  is  sinking  fast;  it 
has  already  descended  to  40°;  it  now  stands  stationary  at  32°;  and  now  crys- 
tals of  ice  are  actually  beginning  to  shoot  out  all  over  the  surface  of  the  water. 
How  beautiful  it  is!  The  surface  is  now  entirely  frozen,  hut  the  thermome- 
ter remains  at  32  degrees. 

•Mrs  B.  And  so  it  will,  conformably  with  our  doctrine  of  latent  heat, 
until  the  whole  of  the  water  is  frozen;  but  it  will  then  again  begin  to  de- 
scend lower  and  lower,  in  consequence  of  the  evaporation  which  goes  on 
even  from  the  surface  of  the  ice  itself(16). 

Emily.  This  is  a  most  interesting  experiment;  but  it  would  he  still 
more  satisfactory  if  no  sulphuric  acid  were  required. 

Mrs  B.  The  method  of  forming  ice  which  I  have  just  shown  you,  was 
contrived  by  Mr  Leslie,  the  inventor  of  the  differential  thermometer;  but  I 
will  show  you  a  freezing  instrument,  contrived  by  Dr  Wollaston,  upon  the 
same  principle  as  Mr  Leslie's  experiment,  and  by  which  water  may  be  frozen 
by  its  own  evaporation  alone,  without  the  assistance  of  sulphuric  acid. 

It  is  exactly  similar  in  its  form  to  the  instrument  invented  by  the  cele- 
brated Dr  Franklin,  which  is  sometimes,  though  very  improperly,  called  a 
jpulse  glass;  it  would  more  properly  be  termed  a  palm  glass. 

This  is  Franklin's  instrument.  It  con- 
tains some  alcohol  Coloured  red;  and  as  the. 
air  is  exhausted  from  it,  there  is  a  strong  ten-^ 
dency  in  the  alcohol  to  evaporate.  If  I  grasp 
one  of  the  bulbs  in  the  palm  of  my  hand,  its 
warmth  will  expand  the  vapour,  and  drive  the 


[Palm,  or  Boiling  Glass.] 


whole  of  the  liquid  into  the  other  bulb,  where,  by  the  passing  of  the  vapour 
through  it,  it  will  assume  the  appearance  of  boiling.  At  this  instant,  a  distinct 
sensation  of  cold  will  be  felt  in  my  hand,  in  consequence  of  the  film  of  alco- 


15.  Of  what  do  the  bubbles  which  first  escape  consist? 

16.  How  is  the  temperature  affected  in  the  progress  of  the  experiment? 


80  CONVERSATIONS  ON  CHEMISTRY. 

hoi  within  the  bulb  becoming  vapour,  and  in  so  doing  absorbing  calo- 
ric(17). 

The  instrument  invented  by  Dr  Wollaston  is,  as  you  see,  much  larger 
than  the  palm  glass,  its  length  being  four  or  five  times  as  great.  Like  the 
latter  its  tube  is  terminated  at  each  extremity  by  a  bulb,  one  of  which 
is  half  full  of  water.  It  is  also  perfectly  exhausted  of  air,  and  consequently 
the  water  in  the  bulb  is  always  much  disposed  to  evaporate.  This  eva- 
poration, however,  does  not  proceed  sufficiently  far  to  freeze  the  water, 
because  the  vapour  formed,  presses  upon  the  surface  of  the  liquid  and  stops 
the  process?  but  if  the  empty  bulb  be  cooled  by  some  artificial  means,  so  as 
quickly  to  condense  the  vapour  which  rises  from  the  water,  the'process  may 
thus  be  so  much  promoted  as  to  cause  the  water  to  freeze  in  the  other  bulb. 
Dr  Wollaston  has  called  this  instrument  a  Cryophorus  or  Frost  bearer(l&). 

Caroline.  Cold  seems  to  perform  here  the  same  part  which  the  sulphu- 
ric acid  acted  in  Mr  Leslie's  experiment? 

Mrs  B.  Exactly  so;  but  let  us  try  the  experiment.  I  pass  the  whole 
of  the  water  into  one  bulb,  and  surround  the  other  with  a  freezing  mixture. 
This  will  condense  the  vapour  which  rises  from  the  water  into  ice  in  the 
empty  bulb;  and  the  vacuum  being  thus  kept  up,  the  evaporation  will  soon 
rob  the  water  of  its  caloric,  and  reduce  the  whole  to  the  state  of  ice(19). 


[Dr  Wollaston's  Cryophorus,  with  the  empty  bulb  immersed  in  a  mixture 
of  snow  and  salt,  for  the  purpose  of  condensing  the  vapour.] 

By  a  process  analogous  to  this,  as  well  as  by  employing  certain  freezing 
mixtures,  mercury  itself  maybe  frozen;  although  this  requires  a  reduction  of 
temperature  of  71  degrees  below  the  freezing  point(20) 

Emily.  Then  there  must  be  some  freezing  mixtures  which  produce  a 
oold  much  more  intense  than  the  snow  and  salt. 

J\frs  B.  There  is  a  great  number;  in  some  of  which  ice  or  snow  is 
used,  in  others  the  cold  is  produced  by  the  solution  of  different  salts  in  wa- 
ter, taken  at  the  ordinary  temperature  of  the  atmosphere,  even  in  sum- 
mer(21).  I  will  show  you  one  example  of  this.  I  have  pulverized  ten 
drachms  of  sal  ammoniac,  (muriate  of  ammonia),  ten  drachms  of  salt-petre, 
(nitrate  of  potassa),  and  sixteen  drachms  of  Glauber's  salt,  (sulphate  of  soda), 
•which  I  have  in  three  separate  papers.  In  this  tumbler  I  have  thirty-two 
drachms  (four  ounces)  of  water,  and  in  this  thin  glass  tube  a  portion  of  wa- 
ter which  I  intend  to  freeze.  By  mixing  these  salts  in  the  water,  and  allow- 
ing the  tube  to  stand  in  the  mixture,  the  water  within  it  will  soon  be  frozen. 
The  solid  salts  dissolve  in  the  fluid,  and  in  doing  so  will  reduce  the  tempe- 
rature from  50°  to  as  low  as  4°  above  zero(22). 

When  you  are  better  acquainted  with  the  different  salts  and  acids,  I  will 
show  you  a  table  of  their  effects,  by  which  you  will  see  that  we  can  com- 
mand a  degree  of  cold  of  nearly  100°  below  the  freezing  point. 


17.  Describe  the  structure  and  operation  of  the  palm  glass. 

18.  What  kind  of  instrument  is  the  Cryophorus  ? 

19.  In  what  way  may  the  water  contained  in  it  be  frozen? 

20.  What  is  said  respecting  the  freezing  of  mercury? 

21.  What  is  observed  respecting  freezing  mixtures? 

22.  By  what  salts  may  water  be  readily  frozen  even  in  summer? 


LATENT  HEAT  CONTINUED.  81 

Caroline.  Indeed,  Mrs  B.,  this  subject  of  heat  seems  to  have  introduced 
us  into  a  new  world.  We  have  hitherto  witnessed  all  these  changes  in  the 
temperature,  and  in  the  form  of  bodies,  with  scarcely  any  other  than  the 
simple  impression  that  they  were  produced  by  heat  and  cold;  but  hereafter 
we  shall  be  delighted  to  apply  the  valuable  knowledge  that  we  have  gained, 
in  tracing  these  changes  in  the  atmosphere,  on  the  earth,  and  in  the  water, 
to  their  causes,  and  must  stand  in  perpetual  admiration  of  the  effects  which 
result  from  them, — effects,  of  which,  but  for  your  kindness,  it  is  probable  we 
should  have  remained  forever  ignorant. 

Mrs  B.  I  shall  be  happy,  my  dear  children,  to  live  in  your  recollection 
as  having,  in  some  measure,  contributed  to  the  enlargement  of  your  views 
of  the  works  of  nature;  but  more  happy  still,  should  your  contemplation  of 
these  works  habitually  lead  your  mind's  to  that  of  their  great  Author,  the  be- 
nevolence of  whose  character  is  as  uniformly  displayed  in  them,  as  are  his 
attributes  of  wisdom  and  power. 

As  you  have  now  obtained  a  pretty  general  view  of  the  different  modifi- 
cations of  which  heat  is  susceptible,  I  will,  before  dismissing  this  subject, 
exhibit  to  you  some  further  instances  of  their  application  principally  in  at- 
mospheric changes.  These  have  been  already  incidentally  touched  on,  but 
you  are  now  more  fully  prepared  to  comprehend  them. 

Caroline.  What  an  astonishing  effect  must  be  produced  by  the  evapora- 
tion which  is  constantly  taking  place  from  the  whole  surface  of  the  earth, 
and  from  the  condensation  of  this  vapour  in  the  form  of  dew  or  rain! 

J\frs£.  So  general  and  so  powerful  is  the  influence  from  the  absorption 
and  evolution  of  caloric  in  these  changes  of  form,  that  without  their  mode- 
rating effects  it  is  certain  that  but  a  small  portion  of  our  earth  would  be 
habitable(23).  If,  as  formerly  supposed,  air,  instead  of  heat,  had  been  the 
solvent  of  water,  no  result  of  this  kind  would  have  been  produced;  but,  as 
it  is,  every  particle  of  water  that  is  evaporated,  absorbs  about  1000°  of  ca- 
loric, which,  when  the  water  is  condensed,  are  again  liberated (24).  The 
ancients  supposed  that  the  equatorial  regions  must  be  uninhabitable,  from 
the  intensity  of  the  heat;  but  the  evaporation  is  proportionate  to  this  inten- 
sity, and  the  vapour  so  formed  ascends  and  carries  off  the  heat  in  a  latent 
state.  When  cooled  in  the  upper  regions  of  the  atmosphere,  or  when  wafted 
to  colder  climes,  it  is  condensed,  and,  in  the  form  of  sensible  heat,  gives 
out  the  caloric  which  it  had  absorbed.  Thus  does  invisible  vapour  become 
the  transporter  of  heat  from  the  torrid  to  the  frigid  zones(25). 

Emily.  And  then  the  very  freezing  of  water  itself  must  contribute  to  the 
same  end,  as  this,  also,  in  becoming  solid,  gives  out  its  latent  heat(26). 

Mrs  JB.  The  quantity  of  caloric  thus  communicated  to  the  atmosphere 
by  the  freezing  of  water  is  exceedingly  great.  Count  Rumford  calculated 
that  "  the  heat  given  off  to  the  air,  by  each  superficial  foot  of  water  in  cool- 
ing one  degree,  is  sufficient  to  warm  an  incumbent  stratum  of  air,  forty-four 
times  as  thick  as  the  depth  of  water,  10  degrees(27)."  In  freezing  it  gives 
out  the  140  degrees  which,  in  its  liquid  form,  remained  latent;  this  will  ena- 
ble you  to  form  some  judgment  of  what  must  be  its  influence  while  undergo- 
ing this  change  of  form  from  the  fluid  to  the  solid  state.  When  we  say  that 
water  gives  out  140°  of  heat  in  becoming  solid,  we  mean  that  in  the 


23.  What  is  said  of  the  influence'  of  the  changes  of  form  which  occur  in 
bodies? 

24.  What  it  suits  from  heat,  instead  of  air,  being  the  solvent  of  water? 

25.  How  does  the  formation  of  vapour  operate  in  equalizing  temperature? 

26.  In  what  way  does  the  freezing  of  water  contribute  its  aid? 

27.  What  calculation  of  Count  Rumford  is  stated? 


82  CONVERSATIONS  ON  CHEMISTRY. 


freezing  of  a  given  portion  of  water,  a  pint  or  a  gill  for  example,  as  much 
heat  is  set  free  as  would  elevate  the  temperature  of  an  equal  quantity  of  water 
140  degrees(28). 

We  know  not  how  intense  would  be  the  cold  which  produces  freezing, 
hut  for  this  counteracting  influence;  or  how  oppressive  the  heat  which  pro- 
duces a  thaw,  but  for  the  quantity  rendered  latent  in  the  very  operation. 

Emily.  Pray,  Mrs  B.,  in  what  manner  do  you  account  for  the  formation 
of  dew? 

Jtfrs  B.  Deio  is  a  deposition  of  watery  particles,  or  minute  drops,  from 
the  atmosphere,  precipitated  by  the  coolness  of  the  evening(29). 

Caroline.  This  precipitation  is  owing,  I  suppose,  to  the  cooling  of  the 
atmosphere,  which  prevents  its  retaining  so  great  a  quantity  of  watery  va- 
pour in  solution  as  during  the  heat  of  the  day. 

JITrs  B.  Such  was,  from  time  immemorial,  the  generally  received  opi- 
nion respecting  the  cause  of  dew(30);  but  it  has  been  very  recently  proved 
by  a  course  of  ingenious  experiments  of  Dr  Wells,  that  the  deposition  of 
dew  is  produced  by  the  cooling  of  the  surface  of  the  earth,  which  he  has 
shown  to  take  place  previously  to  the  cooling  of  the  atmosphere;  for  on  ex- 
amining the  temperature  of  a  plot  of  grass  just  before  the  dew-fall,  he  found 
that  it  was  considerably  colder  than  the  air  a  few  feet  above  it,  from  which 
the  dew  was  shortly  after  precipitated(Sl).  This  fact  accounts  very  satis- 
factorily for  the  formation  of  white,  or  hoar  frost.  Whilst  the  temperature 
of  the  air  is  above  the  freezing  point,  that  of  certain  articles  on  the  surface 
of  the  earth  becomes  sufficiently  reduced  to  condense  and  freeze  the 
moisture  which  was  contained  in  the  atmosphere(32). 

Emily.  But  why  should  the  earth  cool  in  the  evening  sooner  than  the 
atmosphere? 

J\frs  B.  Because,  by  radiation,  it  parts  with  its  heat  more  readily  than 
the  air.  The  earth  is  an  excellent  radiator  of  caloric,  whilst  the  atmosphere 
does  not  possess  that  property,  at  least  in  any  sensible  degree.  Towards 
evening,  therefore,  when  the  solar  heat  declines,  and  after  sun-set,  when  it 
entirely  ceases,  the  earth  rapidly  cools  by  radiating  heat  towards  the  skies; 
whilst  the  air  has  no  means  of  parting  with  its  heat  but  by  coming  into  contact 
with  the  cooled  surface  of  the  earth,  to  which  it  communicates  its  calo- 
ric(33).  Its  solvent  power  being  thus  reduced,  it  is  unable  to  retain  so 
large  a  portion  of  watery  vapour,  and  deposites  those  pearly  drops  which  we 
call  dew,  or  those  glittering  gems  of  which  hoar  frost  consists(34). 

Emily.  If  this  be  the  cause  of  dew,  we  need  not  be  apprehensive  of  re- 
ceiving any  injury  from  it;  for  it  can  be  deposited  only  on  surfaces  that  are 
colder  than  the  atmosphere,  which  is  never  the  case  with  our  bodies. 

J\frs  B.  Very  true;  yet  I  would  not  advise  you  for  this  reason  to  be  too 
confident  of  escaping  all  the  ill  effects  which  may  aris,e  from  exposure  to 
the  dew;  for  it  may  be  deposited  on  your  clothes,  and  chill  you  afterwards 
by  its  evaporation  from  them.  Besides,  whenever  the  dew  is  copious,  there 
is  a  chilliness  in  the  atmosphere  which  it  is  not  always  safe  to  encounter. 

Caroline.  Wind,  then,  should  promote  the  deposition  of  dew,  by  bring- 
ing a  more  rapid  succession  of  particles  of  air  into  contact  with  the  earth, 

— 

.-..'. 

28.  What  is  the  quantity  of  heat  set  free  in  the  freezing  of  water,  and 
what  is  intended  by  so  much  being  set  free? 

29.  What  is  dew,  and  how  is  it  said  to  be  produced? 

SO.  What  opinion  has  been  entertained  respecting  its  precipitation? 

31.  What  observation  of  Dr  Wells  has  led  to  another  theory? 

32.  In  what  way  may  this  apply  to  the  formation  of  hoar  frost? 

33.  How  does  the  earth  cool  to  produce  these  effects? 

34.  Why  does  the  air  then  deposite  moisture? 


LATENT  HEAT  CONTINUED.  83 

just  as  it  promotes  the  cooling  of  the  earth  and  the  warming  of  the  atmosphere 
during  the  heat  of  the  day. 

Mrs  B.  This  may  he  the  case  in  some  degree,  provided  the  agitation 
of  the  air  be  not  considerable;  but  when  the  wind  is  strong,  it  is  found  that 
less  dew  is  deposited  than  in  calm  weather,  especially  if  the  atmosphere  he 
loaded  with  clouds.  These  accumulations  of  moisture  not  only  prevent  the 
free  radiation  of  the  earth  towards  the  upper  regions,  but  themselves  radi- 
ate towards  the  earth;  for  which  reasons  much  less  dew  is  formed  than  on 
fine  clear  nights,  when  the  radiation  of  the  earth  passes  without  obstacle 
through  the  atmosphere  to  the  distant  regions  of  space,  whence  it  receives 
no  caloric  in  exchange(35).  The  dew  continues  to  be  deposited  during  the 
night,  and  is  generally  the  most  abundant  towards  morning,  when  the  con- 
trast between  the  temperature  of  the  earth  and  that  of  the  air  is  greatest. 
After  sunrise  the  equilibrium  of  temperature  between  those  two  bodies  is 
gradually  restored  by  the  solar  rays  passing  freely  through  the  atmosphere 
to  the  earth;  and  later  in  the  morning  the  temperature  of  the  earth  gains  the 
ascendency,  and  gives  out  caloric  to  the  air  by  contact,  in  the  same  manner 
as  it  receives  it  from  the  air  during  the  night(36). 

Can  you  tell  me,  now,  why  a  pitcher  filled  with  cold  water  from  a  well  or 
spring,  or  a  bottle  of  wine  taken  fresh  from  the  cellar  (in  summer  particu- 
larly) will  soon  be  covered  with  dew;  and  even  the  glasses  into  which  the 
water  or  wine  is  poured  will  be  moistened  with  a  similar  vapour? 

Emily,  The  bottle  being  colder  than  the  surrounding  air,  must  absorb 
caloric  from  it.  The  moisture,  therefore,  which  that  air  contained  becomes 
visible,  and  forms  the  dew  which  is  deposited  on  the  bottle,  the  heat  pene- 
trating through  the  glass,  which  the  moisture  cannot  do(37). 

Mrs  B.  Very  well,  Emily.  Now,  Caroline,  can  you  inform  me  why, 
in  a  warm  room,  or  close  carriage,  the  contrary  effect  takes  place:  that  is  to 
say,  why  the  inside  of  the  windows  is  covered  with  vapour? 

Caroline.  I  have  heard  that  it  proceeds  from  the  breath  of  those  within 
the  room  or  the  carriage;  and  I  suppose  it  is  occasioned  by  the  windows 
being  colder  than  the  breath,  and,  therefore,  depriving  it  of  part  of  its 
caloric,  and  by  this  means  converting  it  into  watery  vapour(38). 

Mrs  B.  You  have  both  explained  the  facts  extremely  well.  Bodies  attract 
dew  in  proportion  as  they  are  good  radiators  of  caloric,  and  it  is  thus  that 
their  temperature  is  reduced  below  that  of  the  atmosphere.  Hence  we  find 
that  little  or  no  dew  is  deposited  on  rocks,  or  sand;  whilst  grass  and  living 
vegetables,  to  which  it  is  so  highly  beneficial,  obtain  it  in  abundance,  an- 
other remarkable  instance  of  the  bounty  of  Providence(39). 

Emily.  We  read  that  in  some  hot  climates  rain  is  scarcely  known,  and 
that  the  abundance  of  the  dews  serves  to  supply  the  moisture  necessary  to 
vegetation;  but  I  do  not  understand  what  natural  causes  increase  the  dew  in 
hot  weather. 

Mrs  B.  The  more  caloric  the  earth  receives  during  the  day,  the  greater 
will  be  the  evaporation,  and  the  more  its  loss  by  radiation  during  the  night; 
ami  from  both  these  causes  the  greater  will  be  the  deposition  of  the  dew. 


35.  What  is  observed  respecting  the  effect  of  winds  and  clouds? 

36.  What  is  the  process  at  night  and  in  the  morning? 

37.  What  causes  the  dew,  or  moisture,  upon  a  vessel  containing  a  cold 
liquid,  in  a  warm  room? 

38.  What  causes  (he  moisture  on  the    inside  of  the  windows,  in  cold 
weather? 

39.  Why  is  dew  deposited  on  some  bodies  more  than  upon  others? 


94  CONVERSATIONS  ON  CHEMISTRY. 


During  a  calm  and  clear  night,  a  thermometer  on  the  ground  may  be  12° 
lower  than  one  hung  in  the  air,  owing  entirely  to  this  free  radiation(40).  \ 

Caroline.  I  have  been  thinking  of  the  formation  of  clouds.  I  understand 
very  well  that  they  consist  of  the  watery  vapour  which  rises  from  the  earth, 
and  is  partially  condensed;  but  frequently  they  form,  and  appear  very  dense, 
and  again  disappear  with  great  rapidity,  not  producing  rain,  but  seeming 
to  vanish  entirely. 

Mrs  B.  The  causes  of  the  changes  which  occur  in  the  atmosphere,  and 
•which  are  studied  under  the  name of  Meteorology{k\. ),  have  puzzled  wiser 
heads  than  ours.  They  take  place  in  regions  too  elevated,  and  are  effected  by 
circumstances  too  distant  from  us  to  admit  of  accurate  investigation.  They 
are  undoubtedly  governed  by  the  laws  which  have  been  explained  to  you; 
but  from  the  causes  named,  we  can,  in  this  case,  make  only  a  general  appli- 
cation of  these  laws(42).  Currents  of  warm  and  of  colder  air  exist  in  the 
atmosphere.  Whilst  the  quantity  of  heat  is  sufficient,  the  vapour  is  held  in  a 
state  of  perfect  solution;  when  partially  cooled,  a  condensation  into  clouds 
is  the  result.  This,  when  it  occurs  on  the  surface  of  the  earth,  we  call  a 
fog(43).  If  the  cooling  influence  is  from  any  cause  increased,  the  quantity  of 
caloric,  which  served  to  keep  the  water  in  a  state  of  vapour,  being  dimin- 
ished, the  watery  particles  approach  each  other,  and  form  themselves  into 
drops  of  water,  which,  being  heavier  than  the  atmosphere,  descend  to  the 
earth(44).  There  are  also  other  circumstances,  and  particularly  the  varia- 
tion in  the  weight  of  the  atmosphere,  the  changes  which  take  place  in  its 
electrical  state,  &c.  which  may  contribute  to  the  formation  of  rain.  This, 
however,  I  have  already  told  you,  is  an  intricate  subject,  into  which  we 
cannot  more  fully  enter  at  present(45). 

Emily.  Snow,  I  suppose,  is  caused  by  the  condensed  rapour  of  the  clouds 
freezing  before  it  is  formed  into  drops(46);  but  how  hail  can  be  produced, 
and  particularly  in  the  hot  weather  of  summer,  I  cannot  even  guess. 

Mrs  S.  You  have  learned  in  your  geography,  that,  even  near  the  equa- 
tor, the  highest  mountains  are  covered  with  perpetual  snow;  and  this  must 
convince  you  that  at  every  season,  in  very  elevated  regions,  the  temperature 
is  below  the  freezing,  point(47).  Hail  is  undoubtedly  occasioned  by  the 
formation  of  drops  of  rain  in  a  warm  stratum  of  moist  air  with  one  that  is 
dry  and  cold  below  it.  In  falling  through  this  latter,  the  drops  freeze,  and, 
from  their  weight,  fall  with  such  rapidity  to  the  earth,  that  the  warm  at- 
mosphere has  not  time  to  produce  any  sensible  effect  upon  them(48). 

Caroline.  I  know  that  those  who  have  ascended  to  a  great  height  in 
balloons,  have  uniformly  borne  testimony  to  the  severity  of  the  cold,  and 
certainly  elevated  mountains  are  every  where  covered  with  snow.  Now  I 
should  have  supposed  that  as  in  ascending  in  mid-day  you  approach  the  sun, 
if  any  difference  were  felt  it  would  be  of  an  opposite  kind. 

Mrs  JB.  At  the  distance  of  nearly  a  hundred  millions  of  miles  from  the 
sun,  the  approach  of  a  few  thousand  feet  could  make  no  sensible  difference 
in  its  effects(49). 


40.  What  occasions  the  abundance  of  dew  at  certain  times  and  places? 

41.  What  is  intended  by  the  term  Meteorology? 

42.  What  circumstances  interfere  with  its  investigation? 

43.  In  what  way  are  clouds  and  fogs  produced? 

44.  How  are  they  made  to  produce  rain? 

45.  What  circumstances  are  supposed  to  influenc^  the  result? 

46.  In  what  way  is  the  vapour  condensed  into  snow? 

47.  What  proves  that  the  cold  is  intense  at  great  heights? 

48.  How  is  hail  supposed  to  be  produced? 

49.  Why  is  not  the  influence  of  the  sun  increased  as  you  ascend  at  noon? 

LI 


LATENT  HEAT  CONTINUED.  85 

The  coldness  of  elevated  stations  is,  however,  dependent  upon  a  general 
law  regarding  radiant  heat,  which  is,  that  radiant  heat  passes  through 
transparent  media  without  heating  them;  and  as  our  atmosphere  is  perfectly 
transparent,  there  is  no  heat  imparted  to  it  from  the  solar  rays,  which  arrive 
through  it  to  the  surface  of  the  earth,  without  any  diminution  of  their  in- 
tensity(50). 

Emily,  But,  Mrs  B.,  if  the  atmosphere  is  not  warmed  by  the  passage  of 
the  sun's  rays  through  it,  how  does  it  acquire  heat? 

Jtfrs  B.  Just  as  heat  was  communicated  to  the  water  which  we  boiled  in 
the  flask  some  time  since.  Opake  bodies  absorb  the  solar  ray  and  become 
heated,  and  these  communicate  their  heat  to  the  portion  of  air  in  contact 
with  them.  It  is  the  earth  therefore  which  warms  the  atmosphere.  The  stra- 
tum of  air  which  is  immediately  in  contact  with  it,  is  heated  by  it,becomes 
specifically  lighter,  and  rises,  making  way  for  another  stratum  of  air,  which 
is,  in  its  turn,  heated  and  carried  upwards;  and  thus  each  successive  stratum 
of  air  is  warmed  by  coming  in  contact  with  the  earth(51).  You  may  per- 
ceive this  effect  in  a  sultry  day,  if  you  attentively  observe  the  strata  of  air 
near  the  surface  of  the  earth.  They  appear  in  constant  agitation;  for  though 
it  is  true  that  the  air  ijself  is  invisible,  yet  the  sun  shining  on  the  earth  ra- 
rifiesthe  air,  which  rising,  mixes  with  that  of  a  greater  density,  in  doing  which 
its  undulatory  motion  is  rendered  visible.  The  temperature  of  the  surface  of 
the  earth  is  therefore  the  source  from  which  the  atmosphere  derives  its  heat, 
though  it  is  communicated  neither  by  radiation,  nor  transmitted  from  one 
particle  of  it  to  another  by  the  conducting  power;  but  every  particle  of  air 
must  come  in  contact  with  the  earth,  in  order  to  receive  heat  from  it(52). 

Caroline.  Yet  as  the  warm  air  rises  from  the  earth,  and  the  cold  air 
descends  to  it,  I  should  have  supposed  that  heat  would  have  accumulated  in 
the  upper  regions  of  the  atmosphere,  and  that  we  should  have  felt  the  air 
warmer  as  we  ascended. 

Mrs  JS.  The  atmosphere,  you  know,  diminishes  in  density,  and  conse- 
quently in  weight,  as  it  is  more  distant  from  the  earth.  The  warm  air,  there- 
fore, i*ises  only  till  it  meets  with  a  stratum  of  air  of  its  own  density;  and  it 
cannot  ascend  into  the  upper  regions  of  the  atmosphere  until  all  the  parts 
beneath  have  been  previously  heated.  Besides,  as  it  ascends  it  becomes 
more  rare,  and  consequently  has  its  capacity  increased,  and  its  sensible  heat 
reduced.  It  is  also  wafted  to  colder  regions,  and  performs  its  office  of  aiding 
in  equalizing  the  temperature  of  the  earth(53). 

Caroline.  Still,  as  the  mountains  which  are  covered  with  snow  are 
similar  to  other  portions  of  the  earth,  it  appears  to  me  that,  according  to  our 
theory,  they  ought  to  become  heated  by  the  solar  rays,  and,  of  course,  have 
the  snow  melted  upon  their  surfaces. 

JMrs  B.  You  must  recollect  that  they  are  surrounded  by  an  ocean  of 
eold  air  in  constant  motion,  which  is  amply  sufficient  to  carry  off  all  the 
heat  which  their  comparatively  small  surfaces  allow  them  to  absorb.  In  the 
upper  regions  the  currents  of  air  are  as  constant,  and  probably  as  regular, 
as  the  tides  in  the  ocean(54). 

Emily.  Is  it  also  a  fact  that  glass,  crystal,  diamond,  water,  and  all  other 
transparent  substances,  allow  the  rays  of  heat  to  pass  through  them  without 
acquiring  any  themselves? 


50.  What  is  the  effect  of  radiant  heat  upon  transparent  media? 

51.  How  is  the  heat  communicated  to  the  atmosphere? 

52.  How  may  the  fact  of  rarefaction  of  the  air  be  observed? 

53.  What  is  consequent  upon  the  ascent  of  heated  air? 

54.  Why  are  high  mountains  but  little  affected  by  solar  heat? 

H 


86  CONVERSATIONS  ON  CHEMISTRY. 

Mrs  B.  If  perfectly  transparent,  this  would  be  the  case.  The  burning- 
glass  collects  the  rays  of  heat  to  a  focus,  and  itself  remains  cool.  If  you  hold 
it  so  that  the  rays  are  concentrated  in  the  middle  of  a  vessel  of  clear  water, 
flie  fluid  will  not  become  heated(55);  but  if  apiece  of  any  opake  substance  be 
placed  at  the  focus,  the  water  may  soon  be  made  to  boil;  or,  if  a  portion  of 
ink,  or  of  any  article  which  will  impair  its  transparency,  be  mixed  with  the 
•water,  it  will  in  like  manner  become  heated  by  means  of  the  glass,  or  by  ex- 
posure to  the  rays  of  the  sun(56).  The  most  simple  way  of  trying  this  ex- 
periment is  to  expose  two  bowls  of  water  to  the  action  of  the  sun,  one  dirty 
and  one  clean;  you  will  find  that  the  clean  water  will  remain  the  longest 
cool.  The  containing  vessel  however  must  eventually  become  warm,  and  of 
course  heat  its  contents(57) 

We  must  now  dismiss  the  separate  consideration  of  the  subject  of  heat} 
but  we  shall  find  it  accompany  us  through  all  our  chemical  inquiries,  in 
connexion  with  every  change  which  you  will  witness.  You  will  conse- 
quently be  compelled  to  advert  to  the  laws  which  have  been  explained  to 
you,  with  a  frequency  which  must  render  them  perfectly  familiar.  Our  next 
conversation  will  be  on  electricity. 


CONVERSATION  VIII. 

ON  ELECTRICITY. 

Name.  Appearances  produced  by  Friction.  Opinions  respecting  its 
Nature.  Jlnalogy  toith  Heat.  Positive  and  Negative.  Theory  of  a  single 
and  of  two  Fluids.  Electrical  Machine.  Conductors  and  Non-conductors, 
Spark  and  Shock.  Leyden  Jar.  Insulation.  Induction.  Franklinian 
theory  of  the  Leyden  Jar.  Lightning  and  Thunder. 

Caroline.  I  feel  a  great  deal  of  interest  in  the  subject  upon  which  we 
are  now  to  converse;  for  although  I  have  repeatedly  witnessed  electrical  ex- 
periments, and  have  read  something  respecting  them,  electricity  is  still  to 
ine  a  subject  of  much  mystery. 

J\frs  B.  Nor  can  I  promise  entirely  to  draw  aside  the  veil  which  now 
obscures  it;  for  notwithstanding  enough  is  known  about  it  to  convince  us  that, 
like  caloric,  it  is  an  agent  universally  diffused,  and  of  perpetual  operation, 
yet  of  its  intimate  nature  we  cannot  be  said  to  know  any  thing(l).  Some 
believe  it  to  be  simple,  others  view  it  as  compound,  and  although  it  is  gene- 
rally denominated  a  fluid,  there  are  eminent  philosophers  who  have  doubted 
its  being  a  material  agent,  believing  it  probable,  that,  like  attraction,  it  is  a. 
mere  property  of  matter(2).  It  is  necessary^  however,  for  us  to  adopt  some 
theory,  for  the  purpose  of  connecting  together  the  valuable  and  numerous 
facts  which  have  been  discovered  respecting  it;  but  let  me  enjoin  it  upon 
you  to  use  this  theory  only  as  you  would  an  artificial  memory,  to  enable  you 
to  recollect  what  without  its  aid  might  be  forgotten(S). 

Caroline.     I  confess,  Mrs  B.,  that  my  ardour  begins  already  to  abate,  for 


55.  What  is  remarked  respecting  a  burning-glass^ 

56.  How  may  water  be  heated  by  such  a  glass? 

57.  How  may  the  same  fact  be  proved  without  a  glass? 

1.  What  is  said  of  the  electric  fluid,  and  of  our  acquaintance  -with  it? 

2.  What  different  opinions  are  entertained  respecting  it? 

3.  What  is  the  proper  use  of  a  theory? 


ON  ELECTRICITY.  87 

how  can  we  feel  any  great  interest  in  a  science  in  which  we  know  that  so 
much  uncertainty  prevails.  I  like  those  which  rest  upon  established  prin- 
ciples, and  which,  when  we  have  once  learned,  we  have  learned  forever. 
I  was  in  hopes  that  the  new  discoveries  in  electricity  had  thrown  so  great  a 
light  on  the  subject,  that  every  thing  respecting  it  would  have  been  clearly 
explained;  but  it  seems  that  whilst  we  are  informing  ourselves  concerning 
it,  we  ought  to  think,  all  the  time,  that  perhaps  what  we  are  so  eager  to 
learn  is  not  true. 

JWrs  B,  When  we  dismiss  our  sober  reason  and  allow  our  ardour  to  run 
into  enthusiasm,  we  are  not  in  the  right  road  for  the  discovery  of  truth. 
The  facts  which  you  will  learn  are  not  the  less  true  because  your  powers 
are  limited,  and  you  therefore  cannot  discover  their  remote  causes.  You 
were  satisfied,  in  your  natural  philosophy,  to  refer  a  great  number  of  opera- 
tions to  gravitation;  yet  of  the  cause  of  gravitation  you  do  not  pretend  to 
know  any  thing.  If  you  must  have  absolute  certainty,  you  must  relinquish 
the  physical  sciences,  and  devote  yourself  to  the  pure  mathematics,  where 
every  thing  is  as  certain  as  that  two  and  two  make  four;  yet  of  the  mathe- 
matics you  will  confess  that  you  were  not  very  fond,  although  you  have  made 
some  progress  in  the  study  of  them(4). 

Caroline,  Thank  you,  my  dear  madam,  for  your  rebuke,  the  justice  of 
which  I  feel,  and  will  endeavour  to  profit  by  it.  I  believe  the  science  of 
electricity  is  of  modern  origin,  and  therefore  we  ought  not  to  look  for  as 
much  perfection  in  it,  as  in  some  others. 

Mrs  JB.  The  ancients  had  noticed  that  certain  bodies,  by  being  rubbed, 
acquired  the  property  of  first  attracting  and  afterwards  repelling  light  sub- 
stances. One  of  the  articles  which  does  so  in  an  eminent  degree  is  amberj 
and  from  electron,  the  Greek  name  of  amber,  the  term  electricity  is 
derived(5).  There  are  many  other  substances  which  possess  this  property; 
among  them  are  glass,  the  resins,  sulphur,  wax,  jet,  silk,  fur,  and  woollen(C). 
I  rub  this  large  glass  tube  with  a  silk  handkerchief,  and  you  see  that  it 
first  attracts,  and  afterwards  repels  this  flock  of  cotton.  The  same  effect  yon 
perceive  takes  place  on  rubbing  this  stick  of  sealing  wax  with  a  piece  of 
dry  flannel.  If,  after  thus  rubbing  them,  you  present  your  knuckle  to  either 
of  them,  you  will  feel  a  slight  sensation,  and  hear  a  hissing  noise.  Were  you 
in  the  dark,  you  would  likewise  see  flashes  of  light  between  the  glass,  or 
sealing  wax,  and  the  knuckle.  These  are  denominated  electric  appear- 
ances(7). 

Emily.  I  have  frequently,  in  frosty  weather,  noticed  similar  appearances 
in  parts  of  my  dress,  particularly  in  flannel  and  silk,  and  have  sometimes 
felt  a  smart  sensation  from  the  sparks  which  have  been  emitted(S). 

J\frs  B.  The  friction  of  woollen  against  silk  often  excites  electric  ap- 
pearances very  strongly;  and  after  becoming  familiar  with  the  subject,  you 
will  notice  numerous  other  cases  in  which  similar  effects  take  place.  Eleo- 
tricity  is  now  generally  regarded  as  a  very  subtile  elastic  fluid,  present  in, 
all  bodies.  It  is  viewed  as  one  of  the  most  active  principles  in  nature.  It 
is  the  cause  of  thunder  and  lightning,  of  the  phenomena  of  galvanism,  and 
probably  also  of  magnetism.  It  is  so  intimately  concerned  in  chemical 
changes,  as  to  have  given  plausibility  to  the  notion  that  it  is  the  cause  of 
them(9). 


i.  What  is  said  respecting  certainty  in  the  physical  sciences? 

5.  From  what  was  the  name  Electricity  derived? 

6.  What  other  substances  besides  amber  possess  this  property? 

7.  Name  the  appearances  produced  by  rubbing  glass  or  sealing  wax. 

8.  What  does  Emily  mention  that  she  has  noticed  ? 

9.  What  is  observed  respecting  its  nature  and  effects? 


88  CONVERSATIONS  ON  CHEMISTRY. 

CaroKne.  If  it  is  a  principle  so  active,  and  so  universally  diffused,  ought 
we  not  constantly  to  be  sensible  of  its  influence?  Yet  this  appears  to  be 
rarely  the  case. 

Mrs  B.  Perhaps  you  will  he  more  sensible  of  its  influence  when  you 
are  more  familiar  with  its  effects;  as  you  can  now  detect  the  influence  of 
heat  in  cases  where  you  did  not  formerly  suspect  it.  If  heat  were  equally 
diffused  throughout  all  the  bodies  in  nature,  what  means  would  you  possess 
of  knowing  its  effects? 

Emily.  I  cannot  perceive  how,  in  that  case,  we  could  even  know  of  its 
existence,  or  what  idea  we  could  have  of  heat  and  cold,  as  the  temperature 
of  all  bodies  would  be  alike;  or  rather  there  would  be  no  such  thing  as  tem- 
perature^ 0). 

Mrs  B.  Very  well  said,  indeed;  your  conclusions  are  quite  logical. 
You  Avill  find  a  strong  analogy  in  many  points  between  caloric  and  the  electric 
fluid;  and  one  instance  of  it  is  furnished  by  the  fact,  that  it  is  only  by  the 
disturbance  of  their  equilibrium  that  we  become  acquainted  with  their  exis- 
tence^ 1).  When  a  body  contains  less  than  its  natural  share  of  the  electric 
fluid,  it  is  said  to  be  negatively  electrified,  and  when  more,  to  be  positively 
electrified;  but  in  either  case  the  body  is  said  to  be  excited(12).  The  best  way 
of  exciting  substances  is  by  friction.  When  two  different  bodies  are  rubbed 
together,  it  appears  that  one  may  possess  the  property  of  parting  with  a  por- 
tion of  its  electricity  to  the  other;  in  which  case  they  will  both  be  excited, 
the  one  negatively,  and  the  othet-  positively(l3).  Thus  in  the  rubbing  of 
the  glass  tube  with  the  silk  handkerchief,  a  part  of  the  electricity  of  the 
silk  attached  itself  to  the  glass.  The  former  therefore  was  in  a  negative,  the 
latter  in  a  positive  state,  and  each  of  them  would  have  exhibited  electrical 
appearances(!4). 

Caroline.  In  my  late  reading  upon  this  subject,  I  had  understood  that 
there  were  two  distinct  fluids,  one  called  negative,  or  resinous  electricity, 
and  the  other  positive,  or  vitreous;  and  that  when  a  body  was  excited  it  con- 
tained an  excess  either  of  the  one  or  the  other(15). 

Mrs  B.  Such  is  the  opinion  of  some  eminent  philosophers,  who  have, 
cf  course,  strong  grounds  upon  which  to  found  their  theory:  this,  however, 
is  a  point  which  we  cannot  discuss  at  present.  Those  who  believe  in  two 
fluids,  teach  that  when  these  fluids  are  united,  no  electrical  appearances  ex- 
ist, but  that  they  neutralize  each  other.  Thus,  according  to  this  opinion,  in 
rubbing  the  silk  and  glass  together,  the  electricity  in  each  was  decomposed; 
the  positive  electricity  of  the  silk  going  over  to  the  glass,  and  the  negative 
electricity  of  the  glass  to  the  silk,  and  each  therefore  contained  an  excess  of 
the  electric  fluid,  but  of  the  opposite  kinds(16). 

Emily.  It  seems  to  me  more  natural  to  admit  of  but  one  electric  fluid, 
and  to  suppose  that  the  negative  state  is  merely  a  privation  of  electricity,  as 
cold  is  a  privation  of  heat,  and  the  positive  state  an  excess  of  it,  like  one 
body  being  hotter  than  another. 

Mrs  B.  The  able  founder  of  this  opinion  was  our  eminent  countryman 
Franklin,  and  I  believe  that  its  supporters  form  a  large  majority  among 
men  of  science(17).  We  must  not,  however,  consider  this  question  as  one 


10.  If  heat  were  equally  diffused,  what  would  be  the  result? 

11.  What  analogy  is 'there  between  heat  and  electricity? 

12.  When  is  a  body  said  to  be  negatively,  and  when  positively  electrified? 

13.  When  electricity  is  excited  by  friction,  what  is  believed  to  occur? 

14.  How  is  this  exemplified  in  rubbing  glass  with  silk? 

15.  What  does  Caroline  observe  that  she  had  read? 

16.  What  is  the  outline  of  the  theory  of  two  fluids? 

17.  Who  was  the  founder  of  the  theory  of  a  single  fluid? 


ON  ELECTRICITY.  89 

that  may  be  settled  by  votes,  or  ourselves  undertake  to  become  judges 
upon  such  a  subject.  I  shall  adopt  the  theory  of  a  single  fluid,  because  I 
think  it  the  more  convenient,  and  confess  that  I  am  inclined  to  believe  it  to 
be  the  truth.  This  fluid,  like  heat,  is  repulsive  among  its  own  particles, 
but  attractive  of  other  matter,  and  has  a  tendency  to  an  equilibrium(lS). 

Caroline.  Pray,  Mrs  B.,  what  was  the  origin  of  the'  terms  vitreous  and 
resinous,  which  it  seems  are  synonimous  with  positive  and  negative(W}. 

Mrs  B,  They  were  adopted,  because  glass,  and  other  vitreous  bodies, 
when  rubbed,  generally  become  positively  electrified,  whilst  resinous  sub- 
stances are  thus  rendered  negative.  The  terms  plus  and  minus  are  also 
sometimes  used  to  designate  an  excess  or  a  deficiency  of  this  fluid(20). 

There  are  but  few  subjects  so  fertile  in  striking  facts  and  brilliant  expe- 
riments as  that  of  electricity;  but  we  must  touch  but  lightly  upon  it,  or 
we  should  be  detained  too  long  from  the  pursuit  of  chemistry.  I  will  now 
explain  to  you  the  structure  of  the  common  electrifying  machine  which 
we  have  upon  the  table,  and  you  will  find  it  perfectly  analogous  in  its  ope- 
ration to  the  glass  tube  and  silk  handkerchief. 

Electrical  Machine. 


[A,  The  cylinder.  B,  the  prime  conductor.  C,  the  cushion.  D,  jar  sus- 
pended from  the  prime  conductor  to  receive  a  charge.  E,  insulating  pillar 
of  the  conductor.  F,  insulating  pillar  of  the  rubber,  or  cushion.  G, 
chain  to  connect  the  cushion  with  the  ground,  through  the  medium  of  the 
table,  &c. 

The  back  part  of  the  machine  is  presented  for  the  purpose  of  showing  the 
cushion  distinctly.] 

The  part  called  the  cylinder,  which  is  of  glass,  is  made  to  revolve  by- 
means  of  the  handle,  and  in  so  doing  it  rubs  against  a,  part  at  the  back, 
called  the  cushion,  or  rubber,  which  is  elastic,  and  covered  with  leather.  Dur- 
ing this  revolving  motion,  a  portion  of  the  electricity  of  the  rubber  passes  on 
to  the  surface  of  the  glass,  which,  having  an  excess,  will  readily  part  with  it 
to  any  conducting  substance  presented  to  it.  Thus  if  you  present  your  knuckle, 


1.8.  What  attractive  and  repulsive  properties  is  this  fluid  said  to  possess? 

19.  What  terms  are  used  synonimously?  « 

20.  In  what  did  these  terms  originate,  and  what  others  are  employed? 

H2 


90  CONVERSATIONS  ON  CHEMISTRY. 

to  the  side  of  the  glass  opposite  the  cushion,  you  will  not  only  feel,  but 
see  and  hear  the  fluid  passing  from  it  into  your  hand(21). 

Emily.  Then  my  hand  is  a  conductor  of  the  fluid.  Glass,  I  believe,  is 
called  a  non-conductor. 

J\frs  B.  Electricity,  like  heat,  passes  with  facility  along  some  bodies, 
and  very  slowly  indeed  along  others.  The  metals  are  the  best  conductors 
of  electricity,  as  they  are  of  heat  also,  and  the  electric  fluid  passes  along 
them  with  inconceivable  rapidity(22).  All  those  bodies  which  become  ex- 
cited by  friction  are  non-conductors;  for  if  they  conducted  freely,  the  fluid 
would  pass  off"  as  quickly  as  it  was  excited.  They  are  also  called  electrics, 
because  they  become  excited,  or  electrified,  by  friction.  Conductors  are 
also  called  non- electrics,  because  they  are  not  excited  by  friction,  or,  if  ex- 
cited for  a  moment,  have  their  equilibrium  instantaneously  restored  by  their 
conducting  power(23).  But  to  return  to  the  machine. 

Were  we  to  continue  turning  the  cylinder  without  presenting  any  con- 
ductor to  it,  the  fluid  would  pass  round  it,  and  back  again  to  the  cushion. 
But  you  see  in  front  of  it  a  cylinder  of  metal,  with  points  projecting  from  it  to- 
wards the  glass  cylinder.  These  points  receive  the  electric  fluid  with  great 
facility,  and  it  is  immediately  diffused  over  the  prime  conductor,  which  is 
the  name  given  to  this  metallic  body.  You,  well  know  that  very  smart 
sparks  may  be  taken  by  your  knuckle,  or  any  other  good  conductor  which 
is  brought  near  to  it(24). 

Caroline.  When  we  take  a  shock,  a  glass  jar  coated  with  metal  is  al- 
irays  employed.  What  is  the  reason  that  the  pi-ime  conductor  alone  will  not 
give  a  shock  when  the  machine  is  in  action?  I  have  often  tried  it,  but  never 
with  success. 

Jlfrs  B.  From  its  elasticity,  resulting  from  the  repulsion  among  its  own 
particles,  the  electric  fluid  is  constantly  flying  off  from  the  prime  conduc- 
tor into  the  atmosphere.  The  quantity  that  can  be  retained  by  this  part  of  the 
machine  is,  th&refore,  very  limited,  and  affords  no  more  than  what  is  deno- 
minated the  spark(25).  The  electrical  jar,  or  Ley  den  phial,  as  it  is  frequently 
called,  serves  as  a  reservoir,  in  which  the  fluid  can  be  retained  in  a  state  of 
comparative  quiescence.  You  may  frequently  obtain  sparks  from  the  conduc- 
tor to  your  hand  at  the  distance  of  several  inches,  whilst  a  jar  which  may 
contain  a  thousand  times  the  quantity,  must  be  approached  within  half  an 
inch  in  order  to  its  discharge.  I  wi-11  presently  explain  to  you  the  Franklinian 
theory  of  the  action  of  the  jar(26). 

:.  Emily.  The  prime  conductor  is  placed  upon  a  pillar  of  glass.  This,  I 
suppose,  is  because  glass  is  a  non-conductor,  and  serves  therefore  to  prevent 
the  escape  of  the  fluid(27);  but  I  do  not  understand  why  the  cushion  is  also 
placed  upon  a  glass  pillar,  as  this  is  intended  to  supply  the  fluid  to  the 
cylinder. 

Mrs  B.  You  have  judged  correctly  of  the  use  of  the  pillar  of  the  prime 
conductor.  A  conducting  substance  placed  upon  glass,  or  upon  any  other 
non-conductor,  is  said  to  be  insulated,  that  is,  its  communication  with  bodies 
which  would  carry  away  any  electricity  communicated  to  it,  is  cut  off.  A 
perfeon  standing  upon  a  stool  with  glass  legs,  or  upon  a  cake  of  wax  or  rosin, 


21.  Describe  the  structure  and  operation  of  the  electrifying  machine. 

22.  What  is  said  respecting  conductors  and  non-conductors? 

23.  What  bodies  are  called  electrics,  and  what  non-electrics? 

24.  What  further  is  said  of  the  machine,  and  its  prime  conductor? 

25.  Why  can  nothing  more  than  a  spark  be  obtained  from  it? 

26.  What  is  remarked  respecting  the  Leyden  jar? 

27.  What  supports  the  prime  conductor,  and  why  is  it  so  placed? 


ON  ELECTRICITY. 


or  any  body  that  is  suspended  by  threads  of  silk,  is  insulated(28).  In  the 
ordinary  use  of  the  machine  the  cushion  is  not  insulated.  You  perceive  that  a 
brass  chain  hangs  from  it  connecting  it  with  the  table.  This  is  to  afford  to  it  a 
supply  of  the  fluid,  as  it  becomes  exhausted  by  the  turning  of  the  cylinder. 
The  glass  pillar  is  placed  there,  in  order  that  it  may  be  readily  insulated  for 
the  purpose  of  performing  experiments  with  negative  electricity.  If  you  re- 
move the  chain,  the  native  electricity  of  the  cushion  -will  be  carried  off  by 
the  cylinder  and  the  prime  conductor,  and  the  cushion  will  be  in  a  negative 
state,  ready  to  receive  sparks  from  your  hand,  or  from  any  conducting  sub- 
stance presented  to  it(29). 

Caroline.  When  I  present  my  knuckle  to  the  prime  conductor,  or  to 
the  brass  knob  of  the  cushion  after  removing  the  chain,  the  sensation  and 
the  appearances  are  the  same;  the  rapid  motion  of  the  spark  not  allowing 
me  to  tell  whether  it  flies  from,  or  to,  my  knuckle.  By  what  means  then  am 
I  to  discover  whether  a  body  be  electrified  negatively,  or  positively(SO)? 


Mrs  S.  This  can  be  done  with  great  facility. 
Two  bodies  which  are  in  the  same  electrical 
state,  either  negative  or  positive,  repel  each  other, 
whilst  those  which  are  in  opposite  states  attract 
each  other.  When  I  hang  this  thread,  -with  a 
cork  ball  at  each  of  its  ends,  across  the  prime  con- 
ductor, and  turn  the  machine,  they  immediately 
recede  from  each  other,  both  being  positively  elec- 
trified. If  I  hang  a  similar  pair  of  balls  upon  the 
knob  of  the  cushion,  they  also  will  repel  each  other, 
both  being  in  a  negative  state;  but  one  of  those  Q^~  g| 

upon  the  prime  conductor  would  be  very  strongly  {          ^  Q{.      h  Qr  cQrk 
attracted  by  one  upon  the  cushion,   they  being  m     sus'ded   £      a  thread 
opposite  states.     In  order  therefore  to  ascertain     f     ^  ,,        ^   JA     .  ,„  »  n 
whether  a  body  be  positively  or  negatively  elec-     fr°m  the  conductor  *0 
trifled,  all  that  is  necessary  is  to  suspend  a  cork  ball  by  a   silk  thread,   and 
then  to  communicate  electricity  to  it  by  allowing  it  to  touch  the  prime  con- 
ductor, from  which  it  will  receive  positive  electricity.     This  ball  will  then  be 
repelled  by  a  body  positively  electrified,    and  attracted  by  one   negatively 
electrified(Sl).     There  are  also  some  very  delicate   instruments  made  for 
this  purpose,  which  are  denominated  electroscopes,  or  electrometers^^"). 

Caroline.  I  do  not  clearly  understand  what  is  meant  by  electricity  by 
induction.  It  is  spoken  of,  in  the  books  which  I  have  read,  as  always  taking 
place  when  an  electrified  body  approaches  one  which  is  in  its  natural  state. 
There  seems  to  be  something  in  it  very  difficult  to  comprehend(SS). 

•Mrs  B.  I  was  about  to  call  your  attention  to  that  point,  as  it  is  essential 
to  the  understanding  of  the  mode  in  which  the  electrical  jar  receives  its 
charge.  We  have  considered  the  electrical  fluid  as  being  repulsive  of  itself, 
and  as  moving  with  great  facility  through  conducting  substances.  When 
you  place  your  knuckle  near  to  the  positively  electrified  conductor,  your 
knuckle  will  become  negatively  electrified;  a  portion  of  its  native  electricity 
being  driven  out  of  it,  and  made  to  retire  into  your  arm,  by  the  repulsive 
agency  of  that  contained  in  the  conductor.  Your  knuckle  is  thus  prepared  to 


28.  What  is  meant  by  insulation?  and  give  the  examples. 

29.  What  is  the  object  of  insulating  the  cushion? 

30.  Can  the  direction  of  the  electric  spark  be  perceived? 

31.  How  may  we  discover  the  state  of  an  electrified  body? 

32.  What  are  the  instruments  called,  which  are  used  for  this  purpose? 

33.  When  does  a  body  become  electrified  by  induction] 


92 


CONVERSATIONS  ON  CHEMISTRY. 


receive  the  spark,  which,  if  it  he  sufficiently  near,  will  fly  to  it,  in.  order  to 
restore  the  equilibrium(34).  Whenever  a  body  positively  electrified  is 
made  to  approach  another  in  its  natural  state,  it  always  occasions,  or  induces, 
the  contrary  or  negative  state  in  the  latter;  and  it  is  therefore  said  to  be  elec- 
trified by  induction,  whilst  the  former  was  electrified  by  communication(35). 

Emily.  It  seems  strange  that  a  body  should  become  electrified  without 
either  losing  or  receiving  electricity;  as,  if  it  does  neither  the  one  or  the 
other,  it  must  still  possess  its  natural  share. 

Mrs  B.  Your  objection  appears  natural,  but  still  I  think  that  by  calling 
caloric  to  our  aid,  for  the  purpose  of  comparison,  it  will  be  easily  obviated. 
If  you  take  a  bar  of  iron,  and  reduce  the  temperature  of  one  of  its  ends 
ten  degrees,  and  heat  the  other  in  the  same  proportion,  will  its  absolute 
quantity  of  caloric  be  changed(36)? 

Caroline.  Certainly  not;  and  I  now  think  that  I  see  through  the  mys- 
tery. The  repulsive  agency  of  the  electricity  in  the  charged  body  causes  a 
portion  of  that  in  the  second  body  merely  to  retire  back;  but  it  would  then 
seem  that  this  retiring  portion  must  produce  the  positive  state  in  the  part 
to  which  it  is  driven(37). 

Mrs  B.  Your  reasoning  is  perfectly  correct,  and  easily  verified  by  expe- 
riment. I  have  here  a  second  conductor,  insulated  like  the  prime  conductor. 
Upon  each  end  of  this  I  have  hung  cork  balls,  and  upon  placing  it  within  the 
influence  of  the  charged  prime  conductor,  but  not  sufficiently  near  to  receive 
any  of  its  electricity,  both  pair  of  balls  will  exhibit  repulsion;  but  upon 
testing  them  we  shall  find  that  those  which  are  nearest  to  the  prime  conduc- 
tor are  negatively  electrified,  whilst  the  more  distant  pair  are  in  a  positive 
state(38). 


Positive. 


Negative.     Positive. 


[a,  Prime  conductor  of  the  Electrical  Machine,  positively  electrified.  bt 
a  second  insulated  conductor,  with  pairs  of  pith  balls  suspended  at  each 
end.] 

Emily.  That  is  a  very  satisfactory  experiment  indeed,  and  makes  the 
whole  perfectly  plain.  Upon  removing  this  second  conductor  away,  out  of 
the  influence  of  the  machine,  the  fluid  within  it  will  of  course  again  distri- 
bute itself  equally,  and  both  pair  of  balls  will  collapse. 

Mrs  B.  I  now  remove  it,  and  such  you  see  is  actually  the  case(39). 
If  time  admitted  I  would  show  you  some  other  very  satisfactory  illustrations 


34.  What  occurs  as  the  knuckle  approaches  the  conductor? 

35.  Upon  what  general  law  does  this  depend? 

36.  By  what  analogy  is  this  illustrated? 

37.  How  does  Caroline  explain  this  effect? 

38.  By  what  experiment  is  this  fact  exhibited? 

39.  How  may  the  repelling  balls  be  made  to  collapse? 


ON  ELECTRICITY.  93 

of  this  fact;  but  we  must  hasten  to  the  explanation  of  the  Leyden  phial,  so 
called  from  the  discovery  of  it  having  been  ma<k  at  Leyden.  A  glass  bottle, 
or  jar,  is  covered  both  within  and  without,  with  a  metallic  coating,  reaching 
to  within  two  or  three  inches  of  the  top,  where  the  glass  is  left  bare,  so  that 
there  is  no  conducting  communication  between  the  inside  and  the  outside. 
Through  the  neck  of  it  passes  a  brass  wire,  which  touches  the  inside  coat- 
ing, and  having  a  knob  at  its  outer  extremity(40).  If  I  present  this  knob 
to  the  prime  conductor,  the  electric  fluid  will  be  conducted  down  the  wire, 
and  distributed  over  the  inner  surface  of  the  glass  by  means  of  the  metallic 
coating;  a  large  quantity  of  the  fluid  can  be  thus  accumulated,  so  as  to  give 
what  is  called  a  shock(4l).  A  number  of  such  jars  united  together  form 
what  is  called  an  electrical  b after '#(42). 

Caroline.  Then  the  jar  is  charged  by  communication.  From  your  previ- 
ous remarks  I  had  supposed  that  induction  was  in  some  way  concerned  in 
the  process. 

Mrs  B.  You  will  find  that  the  accumulation  depends  entirely  upon  in- 
duction: one  or  two  sparks  would  otherwise  cause  the  jar  to  be  as  highly 
chsrged  as  the  conductor,  and  it  would  therefoi-e  be  as  much  inclined  to  re- 
turn what  it  had  received,  as  to  receive  a  larger  portion.  Glass,  as  well  as 
other  bodies,  is  believed  to  contain,  naturally,  a  large  quantity  of  electricity. 
When  an  additional  portion  passes  into  the  jar,  it  acts  by  its  repulsive  agency 
through  the  glass,  and  drives  off  from  its  outer  surface  an  equal  quantity  of  that 
which  was  naturally  contained  there.  One  side  thus  becomes  negative  by  induc- 
tion, whilst  the  other  becomes  positive  by  communication.  Successive  portions 
are  thus  received,  until  no  more  can  be  expelled  from  the  outer  surface(4S). 

Emily.  It  would  follow  from  this  explanation  that  a  charged  jar,  like  the 
conductor  with  the  two  pair  of  balls,  contained  no  more  electricity  than  it 
did  before  it  was  charged(44). ' 

Mrs  B.  And  such  is  the  theory  proposed  by  Dr  Franklin,  and  received 
by  the  greater  number  of  philosophers.  One  side  is  positively,  and  the 
other  negatively  electrified,  and  the  intervention  of  the  glass  prevents  the 
restoration  of  the  equilibrium.  Sometimes  however  the  force  of  the  charge 
will  be  such  as  to  cause  it  to  perforate  the  glass,  making  a  hole  through  which 
the  fluid  is  discharged.  The  charge  of  the  jar 
will,  of  course,  pass  through  any  conducting 
body  which  forms  a  connexion  between  its 
two  sides.  After  charging  this  jar,  I  place 
one  of  the  knobs  of  a  discharging  rod  against 
the  outside  coating,  and  cause  the  other  to 
approach  the  wire  connected  with  the  inside. 
The  fluid  leaves  the  inside,  passes  along  the 
wire  to  the  outside,  and  the  equilibrium  is 
thus  restored(45). 

Caroline.     And  if  I  take  the  jar  in  one 
hand  and  then  touch  the  knob  with  the  other, 

the  fluid  passes  through  my  arms  and  chest,  [Electrical  jar,  or  Leyden  phial 
and  I  feel  the  shock(46).      I  have  frequently       with  a  discharging  rod. ] 
done  this,  and  knew  that  it  was  necessary  to  touch  both  sides  of  the  jar,  but 
did  not  understand  why   it  was  so.      How  wonderful  i-s  this  fluid,  and  how 


40.  What  is  the  structure  of  the  Leyden,  or  electrical  jar? 

41.  In  what  way  is  it  made  to  receive  the  electric  fluid? 

42.  What  is  meant  by  an  electrical  battery? 

43.  Give  the  general  explanation  of  the  charging  a  jar. 

44.  What  is  said  respecting  the  quantity  of  fluid  in  a  charged  jar? 

45.  What  is  the  mode  of  discharging  a  jar,  and  why? 

46.  How  may  the  shock  be  made  to  pass  through  the  arms? 

^j 


I 
94  CONVERSATIONS  ON  CHEMISTRY. 

interesting  the  study  of  it!    I  shall  never  again  view  experiments  performed  j 
with  the  electrical  machine  as  a  mere  thing  of  amusement,  but  shall  trace  the 
motions  of  the  fluid,  as  I  now  do  that  of  caloric,  in  changes  which  never  be- 
fore engaged  my  attention. 

Emily.  Pray,  Mrs  B.,  why  is  ajar  or  phial  used;  a  bottle  cannot  be  ne- 
cessary to  contain  the  electric  fluid  in  the  way  in  which  it  contains  water? 

J\frs  B.  The  form  is  a  mere  matter  of  convenience.  A  flat  pane  of  glass, 
properly  coated  with  tin  foil  on  each  side,  is  equally  effective,  but  is  more 
easily  broken,  and  not  so  readily  handled,  and  is  therefore  seldom 
used(47). 

I  have  spoken  of  friction  as  the  means  by  which  electricity  is  excited;  but 
you  are  not  to  consider  this  as  the  only  means.  It  appears  to  be  brought  into 
action  by  every  chemical  change.  The  mere  contact  of  two  different  metals 
produces  it;  bodies  become  electrified  by  mere  heating  and  cooling;  evapora- 
tion and  condensation  also  excite  it;  and  it  is  probable  that  upon  this  circum- 
stance depends  the  magnificent  phenomena  of  lightning  and  thunder,  which  we 
so  feebly  imitate  in  our  electrical  experiments(48).  The  clouds  formed  by 
the  partial  condensation  of  the  exhaled  vapours  frequently  become  surcharged 
with  the  fluid;  this  induces  the  contrary  state  in  the  earth  beneath  it,  and  the 
electricity  flies  from  the  cloud  to  the  earth,  exhibiting  a  vivid  light,  and  caus- 
ing those  sounds  which  we  call  thunder,  and  which  is  the  noise  occasioned 
by  the  discharge,  re-echoed  again  and  again  from  the  earth  and  distant  clouds, 
until  lost  in  the  distance(49). 

Emily.  The  air  I  suppose  must  be  a  non-conductor,  or  it  would  restore 
the  equilibrium  as  fast  as  it  was  disturbed. 

JWrs  B.  Were  not  the  air  an  electric,  we  probably  should  know  nothing 
of  the  phenomena  of  electricity.  In  thunder  and  lightning  it  acts  the  part 
of  the  glass  in  the  Leyden  jar:  the  cloud  may  be  considered  as  one  coating 
the  earth  as  the  other,  whilst  the  air  intervening  completes  the  resemblance. 
The  discharge  takes  place  when  the  intensity  of  the  charge  is  such  as  to 
enable  it  to  overcome  the  obstacles  presented  by  distance,  and  the  resis- 
tance of  the  atmosphere(SO). 

You  have  now  learned  enough  respecting  common  electricity  to  be  able  to 
pursue  the  subject  alone,  and  we  must  hasten  to  that  of  Voltaic  Electricity, 
•or  Galvanism,  which,  although  of  very  recent  discovery,  has  so  powerfully 
aided  the  chemist  in  his  researches,  as  almost  to  have  produced  a  revolution 
in  his  science.  We  will  enter  upon  this  subject  to-morrow. 


47.  Is  it  necessary  that  a  jar,  or  bottle,  should  be  employed? 

48.  By  what  means  other  than  friction  may  electricity  be  excited? 

49.  How  is  the  production  of  lightning  and  thunder  explained? 

50.  Is  the  air  a  conductor,  and  what  is  its  influence  in  lightning? 


ON  VOLTAIC  ELECTRICITY.  95 

CONVERSATION  IX. 

ON  VOLTAIC  ELECTRICITY,  OR  GALVANISM. 

Discoveries  of  Galvani.  Discoveries  of  Volta.  Pile,  Trough,  and  Cou- 
ronne  des  tosses.  Motors  of  Electricity.  Action  of  Acids  on  Metals,  ap- 
plied to  the  Trough.  Opinions  of  Volta,  Wollaston,  and  Davy.  Dr  Hare's 
views.  Calorimotor.  Electro-Magnetism.  Thermo-Magnetism. 

Caroline.  I  believe,  Mrs  B.,  that  the  discovery  of  Galvanism,  which  we 
are  to  discuss  to  day,  was  altogether  accidental;  at  least  I  have  seen  it  so 
stated  in  some  accounts  of  it. 

Mrs  B.  And  such  is  the  case,  to  a  certain  extent,  with  almost  every  im- 
portant discovery.  There  is,  however,  frequently  a  want  of  justice  in  as- 
cribing discoveries  to  accident.  Thousands  of  persons  might  have  witnessed 
the  fact  noticed  by  Galvani,  who  would  have  considered  it  as  merely  a  curi- 
ous circumstance,  and  would  have  pursued  it  no  further.  Discoveries  are 
made  in  the  mind  of  the  discoverer.  It  is  the  inquiries  and  researches  sug- 
gested to  the  man  who  possesses  intellectual  acuteness,  and  is  in  the  habit  of 
patient  investigation,  which  give  to  facts  their  value,  as  it  is  by  these  that 
their  influence  and  connexions  are  ascertained. 

Galvani  was  a  professor  of  the  university  of  Bologna,  and  about  the  year 
1790  was  engaged  in  a  series  of  experiments  with  a  view  to  prove  that  mus- 
cular motion  was  intimately  connected  with  electrical  action(l).  Some 
dead  frogs,  intended  to  make  soup  for  his  lady,  who  was  in  ill  health,  were 
lying  upon  a  table  near  an  electrifying  machine.  A  student,  in  the  absence 
of  Galvani,  was  amusing  himself  with  the  instrument,  and  noticed  that  con* 
vulsive  motions  took  place  in  the  muscles  of  one  of  the  frogs,  when  touched 
by  a  piece  of  metal.  This  was  observed,  and  communicated  to  her  husband 
by  Madam  Galvani,  a  lady  of  great  intelligence.  A  series  of  experiments 
•was  instituted  by  the  professor,  who  thought  that  the  facts  which  he  ascer- 
tained lent  powerful  aid  to  the  theory  that  he  had  adopted(2).  He  soon  dis- 
covered the  means  of  exciting  these  contractions  at  pleasure,  by  merely 
using  two  wires  of  different  metals,  independently  of  the  electrical  machine. 
He  afterwards  published  his  discoveries  under  the  name  of  animal  electri- 
city^). 

Emily.  If  the  contractions  were  produced  by  electricity,  I  do  not  see 
why  two  different  metals  were  necessary  to  excite  them;  but  I  suppose  that 
the  mode  of  applying  them  will  explain  the  reason. 

Mrs  B.  The  discovery  of  the  true  theory  of  the  action  of  the  metals 
was  reserved  for  the  celebrated  Signer  Volta  of  Italy,  who  was  of  opinion 
that  the  electricity  did  not  exist  in  the  animal,  but  that  it  was  excited  by 
the  contact  of  the  two  different  metals,  was  by  them  communicated  to  the 
muscle,  and  occasioned  the  convulsive  motions,  just  as  they  may  be  produ- 
ced by  the  ordinary  machirie(4).  The  sense  of  taste,  and  frequently  that  of 
sight,  may  be  very  readily  brought  into  action  in  this  way.  I  have  here  a 


1.  Who  was  Galvani,  and  what  was  his  pursuit  at  the  period  named? 

2.  What  were  the  circumstances  attending  the  discovery  of  Galvanism? 

3.  How  did  he  excite  muscular  contractions? 

4.  Who  discovered  the  true  theory  of  the  action  of  two  metals? 


96  CONVERSATIONS  ON  CHEMISTRY. 

dollar,  and  a  piece  of  zinc  about  the  same  size,  by  which  you  can  try  the  ex- 
periment. If  you  place  the  piece  of  silver  upon,  and  the  zinc  under  your 
tongue,  and  let  the  two  metals  project  so  that  you  can  bring  their  edges  into 
contact,  you  will,  upon  so  doing,  experience  a  very  peculiar  sensation. 

Emily.  Indeed  I  did;  what  a  strong  metallic  taste,  and  I  think  something 
like  heat;  but  I  cannot  describe  it. 

J\frs  B.  If  you  place  one  of  the  pieces  between  the  gums  and  the  upper 
lip,  the  other  between  the  gums  and  the  lower  lip,thenclose  your  eyes,  and 
let  the  metals  touch,  you  will  perceive  the  sensation  of  a  flash  of  light.  There 
are  some  persons,  however,  to  whom  this  is  not  visible(S). 

Caroline.  In  what  way  is  the  contact  of  the  two  metals  supposed  to  pro- 
duce this  effect,  and  is  it  peculiar  to  silver  and  zinc? 

Jlfrs  JB.  By  no  means;  any  two  different  metals  will  produce  it  in  some 
degree,  but  silver  and  zinc  are  among  the  most  effective.  Copper  and  zinc 
however  are  usually  employed,  and  answer  perfectly  well(6).  If  a  plate  of 
copper  and  another  of  zinc  be  insulated,  by  furnishing  them  with  glass  han- 
dles, and  they  then  be  brought  into  contact  by  their  flat  surfaces,  it  will  be 
found  on  separating  them  that  the  copper  will  be  negatively  and  the  zinc 
positively  electrified(7).  It  appears  therefore  that  when  two  different  metals 
are  brought  into  contact,  one  of  them  has  the  power  to  abstract  electricity 
from  the  other,  and  thus  to  become  positively  electrified,  whilst  it  redu- 
ces the  piece  with  which  it  was  in  contact  to  the  negative  state(8).  The  elec- 
tricity from  a  single  pair  of  plates  is  but  feeble,  but  can  be  rendered  perfectly 
sensible  by  means  of  a  delicate  electroscope.  From  this  property  Volta, 
who  was  the  author  of  this  discovery,  denominated  the  metals  motors  of  elec- 
tricity, and  the  process  electro-motion(9). 

Emily.  You  say  that  electricity  from  a  single  pair  of  plates  is  feeble: 
can  it  be  increased  by  using  a  larger  number,  or  in  any  other  way? 

J\frs  B.  Volta,  considering  that  the  zinc  had  the  power  of  moving  some 
of  the  electricity  from  the  copper  into  itself,  imagined  that  if  this  result 
could  be  obtained  through  a  number  of  successive  pairs,  the  effect  would 
be  proportionally  increased;  and  proceeding  upon  this  idea  he  constructed 
the  VOLTAIC  PILE,  of  which  he  published  an  account  in  the  year  1800(10). 
This  pile  he  constructed  by  taking  an  equal  number  of  plates  of  copper, 
of  zinc,  and  of  pieces  of  cloth  cut  a  little  smaller  than  the  metallic  plates. 
The  cloth  he  moistened  in  a  solution  of  salt  in  water;  these  were  piled  upon 
each  other,  by  first  placing  a  piece  of  zinc  on  a  round  block  of  wood,  upon 
that  apiece  of  copper,  and  then  a  moistened  cloth;  this  arrangement  he  con- 
tinued— zinc,  copper,  cloth;  zinc,  copper,  cloth — until  thirty,  forty,  or  fifty 
of  each  were  piled  up.  If  the  pile  began  with  zinc,  it  ended  with  copper; 
the  electro-motive  effect  increasing  with  the  number  of  plates.  It  was  now 
found  that  the  zinc  end  of  the  pile  was  highly  positive,  and  the  copper  end 
highly  negative;  and  if  a  finger  of  one  hand  was  placed  in  contact  with  the 
lower  plate,  and  the  upper  plate  touched  with  the  other  hand,  a  shock  was 
felt  very  similar  to  that  from  the  common  electrifying  machine(ll).  I  have 
not  a  pile  of  this  sort,  because  more  convenient  instruments,  operating  upon 
the  same  principle,  have  been  invented. 


5.  What  effect  may  be  produced  by  two  metals  placed  in  the  mouth  ? 

6.  Is  the  effect  peculiar  to  silver  and  zinc? 

7.  Relate  the  experiment  with  two  metallic  plates. 

8.  How  are  the  plates  thus  brought  into  opposite  electrical  states? 

9.  What  were  the  substances  called  which  possess  this  property? 

10.  What  was  Volta's  reasoning  on  the  subject,  and  to  what  did  it  lead. 

11.  How  did  Volta  construct  his  pile,  and  what  was  the  result? 


ON  VOLTAIC  ELECTRICITY. 

Insulated  plates  of  copper  and  zinc. 
G 


Voltaic  Pile. 
G     GG      G 


Fig.  1. 


Fig.  2. 


[Fig.  1.  Z,  a  plate  of  zinc.  C,  a  plate  of  copper,  each  plate  being  furnished 
with  a  glass  handle,  G,  G,  to  preserve  their  electricity  after  contact. 

Fig.  2.  A,  the  stand  upon  which  the  plates  rest.  C  Z  D,  C  Z  D,  plates 
of  copper  and  zinc,  and  disks  of  moistened  cloth  piled  alternately  upon 
each  other.  G,G,G,G,  rods  of  glass  to  support  the  pile.] 

Caroline.  The  trough  that  you  have  upon  your  table  I  have  heprd  you 
call  the  voltaic  battery,  and  I  suppose  it  is  to  this  which  you  allude  as  being 
more  convenient  than  the  pile. 

Voltaic  Battery. 


[A  trough  with  partitions,  each  formed  of  a  plate  of  copper  and  zinc.] 

J\frs  B.  It  is.  A  wooden  trough  is  made,  and  this  is  divided  into  cells 
by  metallic  partitions,  which  are  cemented  firmly  into  grooves  made  in  the 
trough.  The  metallic  partitions  are  each  formed  by  soldering  together, 
back  to  back,  a  sheet  of  copper  and  a  sheet  of  zinc.  When  these  are  ce* 
mented  into  the  trough,  the  copper  sides  are  all  made  to  face  one  way. 
The  cells  between  the  plates  are  to  be  nearly  filled  with  water,  having  some 
nitric,  or  other  acid,  mixed  with  it(12).  The  resemblance  between  these 
troughs  and  the  pile  must  be  obvious  to  you. 

Emily.  Certainly.  The  zinc  and  copper  are  the  same,  excepting  that 
they  are  soldered  together.  The  fluid  between  them  evidently  supplies  the 
place  of  the  moistened  cloth;  and  the  two  plates  at  the  ends  will,  I  suppose, 
be  in  opposite  electrical  states,  as  you  have  told  us  is  the  case  with  the 


12.  Can  you  describe  the  voltaic  trough,  or  battery? 

13.  In  what  way  may  this  be  compared  with  the  pile? 


98 


CONVERSATIONS  ON  CHEMISTRY. 


Mrs  B.  Very  good.  I  will  now  show  you  another  arrangement,  made 
by  Volta,  which  he  described  in  the  same  paper  in  which  he  made  his  pile 
known.  A  number  of  cups,  or  glasses,  are  placed  side  by  side,  each  of  them 
containing  the  fluid  intended  to  promote  the  electric  action.  These  cups 
are  connected  by  metallic  wires  bent  in  the  way  you  see,  and  having  a  small 
plate  of  zinc  soldered  on  one  end,  and  a  plate  of  copper  on  the  other.  If 
you  observe  how  the  plates  are  placed  in  the  liquid,  you  will  see  that  each 
cup,  excepting  those  at  the  ends,  has  one  plate  of  zinc  and  one  of  copper  im- 
mersed in  it,  in  regular  series.  If  you  dip  a  finger  of  each  hand  into  the 
extreme  cups,  a  shock  will  be  received.  This  arrangement  Volta  denominat- 
ed the  Couronne  des  Tasses(lk). 

Couronne  des  Tasses. 


C,  plates  of  copper. 


Z,  plates  of  zinc. 


Caroline.  How  pungent  the  sensation,  yet  I  do  not  think  it  half  so  unplea- 
sant as  one  of  equal  strength  from  the  electrifying  machine.  I  do  not  see 
why  the  name  of  couronne  was  given  to  this  arrangement. 

Mrs  B.  When  the  cups  are  numerous,  in  order  to  bring  the  two  end 
ones  near  to  each  other,  they  are  usually  so  placed  as  to  form  a  circle;  it  was 
this  arrangement  which  suggested  the  name(15).  There  is  another  very 
convenient  mode  of  constructing  the  trough,  or  battery,  as  it  is  frequently 
called,  which  has  many  advantages,  and  which  you  will  perceive  strongly 
i-esembles  the  couronne  des  tasses.  The  trough  is  made  of  earthemvare,  di- 
vided into  cells  by  partitions  of  the  same  material.  The  plates  of  copper 
and  zinc  are  connected  together  by  a  strip  of  metal  at  the  top  only;  so  that 
both  sides  of  each  plate  may  be  exposed  to  the  action  of  the  acid.  The 
pairs  of  plates  set  like  saddles  upon  the  earthen  divisions,  the  copper  being 
in  one  cell,  and  the  zinc  in  another.  All  the  plates  belonging  to  one  trough 
may  be  fastened  to  a  strip  of  wood,  by  which  they  may  readily  be  taken  out 
of  the  solution  contained  in  the  cells,  and  the  action  of  the  acid  be  conse- 
quently suspended  until  they  are  replaced.  There  is,  as  you  see,  in  this 
trough  a  contrivance  for  hanging  the  plates  over  it(16). 


Voltaic  Battery,  the  Trough  of  Ear  then-war  et  with  the  Plates  out  of  the  Cell*. 


14.  Describe  the  arrangement  called  the  couronne  des  tasses. 

15.  Why  did  this  apparatus  receive  the  name  of  couronne^ 

16.  Describe  the  trough  which  resembles  the  couronne  des  tasses. 


ON  VOLTAIC  ELECTRICITY. 


99 


Section  of  the  Voltaic  battery. 


zc      zc     zc 


zc 


Emily.  The  arrangement  in  each  case  is  manifestly  similar;  but  how  the 
electro-motive  power  operates  through  the  plates  in  producing  the  opposite 
electricities,  is  what  I  do  not  understand,  and  hope  you  will  explain. 

Mrs  JB.  You  must  keep  in  mind  what  we  have  said  upon  the  subject  of 
theory,  and  expect  but  little  in  this  way.  Volta  attributed  the  whole  effect 
to  the  electro-motive  power  of  the  metals;  but  it  is  found  that  when  the  fluid 
used  contains  an  acid  which  will  corrode  and  dissolve  one  of  the  metals, 
the  power  is  very  greatly  increased.  It  appears,  therefore,  that  in  this  case 
a  large  portion  of  the  effect  results  from  chemical  action(17). 

This  drawing  shows  a  section  of  a  part  of  the  trough,  the  construction  being 
of  the  kind  first  described,  and  this  will  serve  to  give  you  a  general  idea  of 
Volta's  theory  of  its  action.  Z  C,  Z 
C,  &c.  represent  pairs  of  copper  and 
zinc  plates,  with  the  fluid  between 
them.  A  portion  of  the  trough  is  seen 
at  the  bottom  and  at  one  end. 

Volta's  theory  of  the  action  of  a 
number  of  pairs,  is  merely  an  exten- 
sion of  the  action  of  a  single  pair. 
The  zinc  plate  1,  being  in  contact 
I  with  the  copper  plate  1,  will  deprive 
the  latter  of  a  portion  of  its  electricity, 
and  will  become  positively  electri- 
fied. The  same  action  must  evidently 
take  place  in  each  of  the  other  pairs, 
2  2,  3  S,  and  4  4.  The  interposed  fluid, 
which  is  an  imperfect  conductor,  will  transmit  from  the  positive  zinc  plate 
1,  a  portion  of  its  excess  to  the  negative  copper  plate  2,  which  had  already 
given  a  part  of  its  own  to  the  zinc  plate  2.  This  will  then,  from  the  electro- 
motive power,  afford  an  increased  portion  to  the  zinc  plate  2,  the  electrical 
state  of  which  will  be  proportionally  exalted.  The  same  reasoning  will 
apply  to  the  plates  3  3  and  4  4,  so  that  the  electrical  energy  will  increase 
with  the  number  in  the  series(18). 

Caroline.  The  explanation,  upon  the  whole,  seems  to  me  clear,  but  I  do 
not  see  why  the  electro-motive  effect  of  the  subsequent  series  should  be 
greater  than  that  of  the  first  pair,  as  it  is  an  innate  power  in  each,  and  arises 
from  the  tendency  in  the  copper  to  give  a  part  of  its  natural  share  to  the 
zinc.  That  each  must  thus  become  electrified  is  plain,  but  I  should  hare 
anticipated  that  they  would  be  so  in  an  equal  degree(19). 

Jlfrs  H.  The  terms  negative  and  positive,  to  borrow  a  simile  again  from 
caloric,  may  be  considered,  like  those  of  hot  and  cold,  to  be  relative  only. 
A  body  at  a  given  temperature  may  be  hot  when  compared  with  one  body, 
but  cold  when  compared  with  another.  Suppose  a  plate  of  copper  to  have 
an  excess  of  electricity  communicated  to  it,  and  to  be  brought  into  contact 
with  a  plate  of  zinc,  then,  from  the  tendency  of  this  fluid  to  an  equilibrium, 
one  half  of  the  excess  would  go  over  to  the  zinc;  but  the  electro-motive 
power  of  the  metals  remaining  unchanged,  another  portion  would  be  com- 
municated to  the  zinc  from  this  cause(20). 

Emily.  It  would  seem  in  this  case  as  though  a  constant  current  of  the 
fluid  would  be  kept  up  as  long  as  the  instrument  lasted,  as  this  electro- 
motive power  must  always  continue  the  same. 


17.  What  is  necessary  to  a  powerful  effect? 

18.  How,  according  to  Volta,  is  the  electricity  accumulated? 

19.  What  objection  does  Caroline  urge  to  the  theory? 

20.  By  what  reasoning  is  this  objection  obT:ated? 


100  CONVERSATIONS  ON  CHEMISTRY. 

J\lrs  J5.  If  wires  be  made  to  connect  the  negative  and  positive  ends,  gene- 
rally called  the  poles  of  the  battery,  a  constant  current  will  be  kept  up;  but 
if  this  connexion  be  interrupted,  the  plates  acquire  a  certain  degree  of  elec- 
tricity, and  then  the  action  must  necessarily  cease(2L).  You  must  not  sup- 
pose, however,  that  under  any  circumstances  this  action  would  be  perpetual. 
It  is  a  fact  that  immediately  after  a  pile  is  put  together,  or  the  fluid  supplied 
to  the  cells  of  a  trough,  the  action  is  the  most  energetic;  but  it  soon  percep- 
tibly diminishes,  and  at  length  becomes  extremely  feeble,  or  altogether  ex- 
tinct(22). 

Caroline.  But  that  does  not  accord  with  the  theory. 
Mrs  B.  It  accords,  however,  with  the/acJ,  and  you  have  not  already  for- 
gotten to  which  of  these  the  greatest  importance  is  to  be  attached?  I  have 
informed  you  that  to  obtain  energetic  action,  a  fluid  must  be  used  which 
•will  corrode  and  dissolve  one  of  the  metals;  and  the  power  of  the  trough 
depends  in  a  great  degree  upon  the  strength  of  this  chemical  action.  The 
theory  of  Volta  is  therefore  defective,  inasmuch  as  it  takes  no  account  of 
this  circumstance(23).  As  you  are  not  yet  acquainted  with  the  nature  and 
action  of  the  acids,  and  of  the  other  agents  employed,  the  information  which 
I  can  give  you  at  present  must  be  very  limited;  but,  as  the  voltaic  battery  is 
a  most  powerful  instrument  in  effecting  decompositions,  we  shall  have  occa- 
sion to  revert  to  it  hereafter,  more,  however,  with  a  view  to  exhibit  its  ac- 
tual power,  than  to  theorize  upon  its  nature. 

Emily.  If  an  acid  is  used  and  the  metal  is  dissolved,  the  apparatus  itself 
must  at  last  disappear,  and  the  copper  and  zinc  both  be  lost. 

J\frs  B.  Recollect  that  an  acid,  if  it  has  an  affinity  for  several  different 
metals,  possesses  it  for  them  in  different  degrees;  and  that,  in  consequence, 
one  may  be  made  to  displace  another  which  is  held  in  solution.  If  two 
metals,  either  of  which  would  be  dissolved  in  an  acid  if  put  into  it  alone, 
be  placed  there  together,  it  will  act  upon  that  to  which  it  has  the  strongest 
affinity,  whilst  the  other  will  remain  nearly  unaffected(24).  The  acids  ge- 
nerally have  a  much  stronger  affinity  for  zinc  than  for  copper,  and  the  zinc 
plates  of  the  voltaic  trough  are  consequently  made  thick,  or  they  would  soon 
require  renewal(25). 

Emily.  Certainly  if  the  zinc  would  separate  the  copper  after  it  had  been 
dissolved,  it  may  well  have  the  power  to  prevent  its  solution.  This  appears 
a  necessary  result,  although  I  do  not  pretend  to  know  any  thing  of  the  cause. 
Caroline.  I  think,  Mrs  B.,  as  this  kind  of  chemical  action  which  takes 
place  between  acids  and  metals,  is  so  intimately  connected  with  that  of  the 
voltaic  battery,  you  might,  perhaps,  by  your  happy  mode  of  explanation,  ena- 
ble us  so  far  to  comprehend  it  as  to  aid  us  in  the  present  inquiry. 

Mrs  B.  This  I  intended,  and  your  anxiety  upon  the  subject  is  a  fair 
omen  of  success.  We  have  only  to  anticipate  a  part  of  the  subject  of  our 
next  conversation,  which  will  embrace  oxygen,  a  principle  entering  into  the 
composition  of  the  greater  number  of  bodies.  The  air  we  breathe  contains 
oxygen,  and  derives  from  it  the  property  of  sustaining  life  and  supporting 
combustion.  It  is  one  of  the  constituents  of  water,  of  which  it  forms  eight 
parts  out  of  nine.  It  is  the  principle  which  communicates  to  most  of  the 
acids  their  sour  taste,  and  their  other  general  properties.  It  is  that  which  in 
a  damp  place  unites  to  iron  or  steel,  and  converts  it  into  rust,  or  what  the 


21.  In  what  way  is  a  continued  current  maintained  in  the  battery? 

22.  Will  the  action  continue  undiminished? 

23.  In  what  point  is  the  theory  of  Volta  defective? 

24.  What  will  follow  if  two  different  metals  be  put  into  the  same  acid? 

25.  What  reason  is  there  for  making  the  zinc  plates  thicker  than  the 


copper 


ON  VOLTAIC  ELECTRICITY.  101 

chemist  denominates  the  oxide  of  iron;  and  in  like  manner  it  may  be  made 
to  unite  with  all  the  metals,  to  some  of  which,  as  to  iron,  ithasa  very  strong 
affinity,  whilst  for  others  its  attraction  is  feeble.  In  fact  the  enumeration 
of  its  habitudes  would  almost  exhaust  the  subject  of  chemistry(26). 

Emily.  I  have  long  been  familiar  with  the  name,  and  had  some  vague 
idea  of  the  nature  of  this  same  oxygen,  and  am  glad  that  we  are  so  soon  to 
be  introduced  to  a  personage  so  extensively  connected;  but  I  am  very  appre- 
hensive that  I  shall  never  become  familiar  with  all  his  relations. 

JWrs  B.  When  a  metal  is  dissolved  by  an  acid,  it  is  first  converted  into 
an  oxide,  and  it  is  this  oxide  which  undergoes  solution(27).  The  oxygen  is 
derived  in  some  cases  from  the  acid,  and  in  others  from  the  water  with  which 
the  acid  is  mixed.  A  solution  of  zinc  in  an  acid  is,  therefore,  strictly  speak- 
ing, a  solution  of  the  oxide  of  zinc,  and  a  solution  of  copper,  a  solution  of 
the  oxide  of  that  metal(28). 

Copper  and  zinc  are  uniformly  employed  for  galvanic  arrangements,  be- 
cause there  are  no  two  metals  equally  energetic  and  cheap;  but  various  other 
combinations  will  answer  the  purpose,  and  in  all  cases  it  is  the  most  oxidi- 
zable  of  the  metals  which  forms  the  positive  pole  of  the  series.  Thus  when 
copper  and  zinc  are  used,  the  zinc  becomes  positive,  and  the  copper  nega- 
tive; but  with  silver  and  copper,  the  latter  would  form  the  positive  pole(29). 

Caroline.  Since  such  important  changes  are  taking  place  both  in  the 
fluid  and  in  the  metal,  I  can  very  well  believe  that  they  must  powerfully  in- 
fluence the  electrical  action  which  results  from  the  electro-motive  power. 

JUrs  J3.  The  late  eminent  Dr  Wollaston  was  of  opinion  that  the  evolu- 
tion of  electricity  was  caused  entirely  by  the  chemical  action,  urging  in  sup- 
port of  it  the  fact  that  they  were  proportionate  to  each  other.  When  water 
alone  is  used  in  the  cells,  the  zinc  is  slightly  and  slowly  oxidized,  and  a 
very  minute  portion  of  electricity  is  disengaged.  When  salt  and  water  are 
employed,  the  oxidation  and  the  electricity  are  both  increased;  and  when 
acids  are  employed,  the  development  of  the  fluid  keeps  pace  with  the  ra- 
pidity of  the  oxidation(SO).  This  theory,  you  perceive,  neglects  the  electro- 
motive power  of  the  metals  altogether,  which,  as  it  does  exist,  seems  to 
claim  a  place  in, the  account(Sl).  Sir  Humphry  Davy  thought  that  the  ex- 
citement was  commenced  in  the  electro-motion, but  was  continued  and  aug- 
mented by  the  chemical  action(32). 

Oxygen  and  certain  analogous  substances  are  always  attracted  towards 
the  positive  pole  of  a  battery.  They  are  therefore  called  electro-negative  bo- 
dies, as  their  natural  electrical  state  in  their  relationship  to  other  bodies  is 
believed  to  be  negative,  and  they  are  therefore  attracted  by  such  as  are 
electro-positive.  The  electro-positive  bodies  are  distinguished  by  their  being 
attracted  towards  the  negative  pole  of  the  voltaic  battery.  This  latter  is  a 
very  large  class,  including  all  the  metals,  and  those  substances  usually  call- 
ed inflammables(33).  These  are  very  important  distinctions,  and  are  fre- 
quently adopted  as  the  foundation  of  chemical  classification(34). 

Emily.     Then  I  suppose  the  oxygen,  which  is  negative,  is  attracted  by 


26.  What  is  said  of  the  combinations  of  oxygen? 

27.  What  combines  with  a  metal  in  order  to  its  being  dissolved  by  an  acid? 

28.  How  does  it  obtain  this  oxygen, and  what  is  said  of  certain  solutions? 

29.  What  is  it  that  determines  the  positive  and  negative  poles' 

30.  What  was  Dr  Wollaston's  opinion  respecting  the  chemical  action? 

31.  This  theory  neglects  an  important  fact,  what  is  that? 

32.  What  did  Sir  Humphry  Davy  suggest  on  this  subject? 

33.  How  are  bodies  denominated,  as  regards  electric  attractions? 

34.  What  is  said  of  these  distinctions? 

I  2 


102  CONVERSATIONS  ON  CHEMISTRY. 

the  zinc,  which  is  positive,  and  that  this  is  a  principal  cause  of  their  combi- 
nation^)? 

J\frs  B.  This  appears  to  be  intimately  concerned  in  their  union;  and  with- 
out admitting  the  suggestion  of  Sir  Humphry  Davy,  that  the  difference  in  the 
electrical  states  is  the  cause  of  chemical  affinity,  it  is  plain  that  it  exerts  a 
powerful  influence. 

The  theory  of  Sir  Humphry  Davy  supposes  that  the  primary  action  of  the 
series  depends  upon  the  electro-motive  power  by  which  the  plates  are  recip- 
rocally rendered  positive  and  negative,  and  that  the  effect  of  the  chemical 
action  is  to  restore  the  plates  to  the  natural  state,  so  that  they  may  repro- 
duce a  fresh  portion  of  the  fluid  by  their  electro-motive  power.  Suppose 
the  acid  in  the  solution  to  be  a  compound  of  oxygen,  which  is  electro-nega- 
tive, with  a  base  which  is  electro-positive,  the  oxygen  will  combine  with  the 
zinc,  which  has  been  rendered  positive,  and  thus  restore  it  to  its  natural 
state;  whilst  at  the  same  time  the  other  constituent  of  the  acid  which 
is  electro-positive  will  be  attracted  by  the  copper,  and  restore  it  also  to 
the  natural  state.  A  new  portion  of  the  electric  fluid  will  then  be  produced 
by  the  action  of  the  metals  upon  each  other.  I  have  been  compelled  to 
describe  these  effects  as  taking  place  alternately,  but  you  will  understand 
that  they  must  be  simultaneous(36). 

Caroline.  Although  there  is  a  good  deal  of  intricacy  in  all  this,  I  think 
that  with  a  little  reflection  1  shall  understand  it;  and,  at  all  events,  I  like  it 
because  it  seems  to  do  justice  to  Volta,  as  it  still  leaves  his  theory  whole, 
and  only  makes  some  addition  to  it.  I  confess  that  I  like  better  to  hear  the 
pile  and  the  trough  called  voltaic  than  galvanic;  for  whatever  might  be  the 
merit  of  Galvani,  Volta  was  the  true  discoverer  of  the  nature  of  the  agent, 
as  well  as  of  the  apparatus  by  which  it  is  exhibited. 

Mrs  B.  I  have  thought  it  right  to  give  you  these  ingenious  speculations, 
which,  as  they  proceeded  from  individuals  who  were  luminaries  in  science, 
are  well  worthy  of  our  attention,  and  are  calculated  to  gratify  a  laudable 
curiosity. 

Emily.  Although  there  is  certainly  considerable  analogy  between  gal- 
vanism and  electricity,  they  yet  seem  so  different  in  several  points  as  to 
leave  some  doubts  of  their  identity.  In  damp  weather  the  electrifying  ma- 
chine will  not  act,  as  you  have  often  told  us,  because  the  moisture  conducts 
off  the  fluid;  yet  your  trough  is  filled  with  moisture  in  order  to  excite  it  into 
action. 

Mrs  B.  There  are  so  many  strong  proofs  of  the  identity  of  the  two  as 
to  leave  no  doubt  upon  the  subject.  A  shock  very  similar  to  that  from  _the 
common  electrifying  machine  is  given  by  the  voltaic  arrangement.  The 
Sftme  substances  which  conduct  the  one,  allow  a  passage  to  the  other.  A 
number  of  individuals  by  joining  hands  will  simultaneously  receive  the 
shock  from  either.  Brilliant  sparks  are  afforded  from  each,  accompanied 
by  a  snapping  noise.  They  produce  combustion  in  the  same  articles.  By 
proper  management  they  effect  similar  chemical  changes.  The  resulting 
attractions  and  repulsions  are  alike;  and  a  common  Leyden  jar  may  be 
charged  by  the  voltaic  battery,  the  charge  being  exactly  similar  to  that  from 
the  common  machine(37). 

Caroline.  This  is  indeed  a  formidable  list  of  resemblances,  and  the  evi- 
dence it  affords  is  irresistible;  still,  as  Emily  says,  it  seems  strange  that  the 


35.  What  influence  has  this  on  the  zinc  plates? 

36.  What  are  the  prominent  points  in  Davy's  theory? 

37.  What  proofs  are  given  of  the  identity  of  the  galvanic  and  electric 
fluids? 


ON  VOLTAIC  ELECTRICITY.  103 

•• 

action  continues  in  the  midst  of  water  and  melals,  which  are  good  conduc- 
tors^ 8). 

J\frs  JB.  The  electric  fluid,  like  caloric,  appears  to  exist  under  different 
modifications.  Caloric  you  know  passes  slowly  along  conductors,  but 
moves  with  immense  velocity  when  radiating  from  the  sun,  or  from  heated 
bodies.  The  solar  heat  passes  readily  through  glass,  whilst  that  from  our 
fires  is  arrested  by  it,  its  projectile  force  appearing  to  be  less  in  the  latter  case 
than  in  the  former.  The  electric  fluid  in  like  manner  possesses  but  little  pro- 
jectile force,  or  intensity,  though  disengaged  in  large  quantity  by  the  voltaic 
apparatus.  Water  and  most  other  fluids  are  but  imperfect  conductors  of  elec- 
tricity, and  may  detain  it  therefore  when  its  intensity  is  but  small;  although 
they  will  conduct  it  off  from  the  common  machine,  whence  it  has  a  great  dispo- 
sition to  escape.  In  consequence  of  this  want  of  intensity,  the  spark  from  a 
powerful  voltaic  battery  will  strike  at  a  very  small  distance  only;  and  it  be- 
comes necessary  to  moisten  the  hands  in  order  to  take  a  shock,  it  not  having 
sufficient  force  to  overcome  the  resistance  of  the  dry  skin(39). 

Emily.  You  have  told  us  that  the  strength  of  the  shock  is  in  proportion 
to  the  number  of  plates;  but  have  said  nothing  respecting  their  size.  As  you 
enlarge  them  the  quantity  of  the  fluid  must  of  course  be  increased. 

Mrs  B.  It  is  a  remarkable  fact,  that  although  the  quantity  of  the  fluid  is 
increased  by  enlarging  the  plates,  yet  the  power  of  the  shock  remains  the 
•ame(40).  This  increased  quantity  however  produces  most  brilliant  com- 
bustions of  the  metals,  and  of  other  inflammables(4l).  By  increased  num- 
bers the  intensity  is  increased,  and  upon  this  the  force  of  the  shock  depends; 
but  in  burning  the  metals,  what  is  principally  required  is  a  large  quantity, 
and  as  they  are  good  conductors,  the  fluid  will  pass  through  them,  although 
its  intensity  may  be  very  low(42). 

From  the  fact  that  when  the  plates  are  large  in  size  and  few  in  number, 
the  electrical  effect  is  feeble,  and  the  calorific,  or  heating,  strong,  and  that 
when  the  number  is  great,  and  their  dimensions  small,  the  reverse  is  the 
case,  Dr  Hare  of  Philadelphia  has  drawn  the  conclusion  that  the  galvanic 
fluid  is  a  compound  of  electricity  and  caloric,  and  that  one  or  the  other 
power  prevails  according  to  the  nature  of  the  apparatus  employed.  He  has 
given  to  the  science  some  powerful  instruments,  particularly  one  which  he 
denominates  the  calori-motor,  intended  to  exemplify  the  justness  of  hiscon- 
clusions(43). 

Caroline.  In  what  way  has  the  voltaic  battery  so  powerfully  aided  the 
chemist  in  overcoming  chemical  attraction,  and  consequently  effecting  de- 
compositions? 

Mrs  B.  It  appears  that  there  is  as  general  a  difference  in  the  electrical 
state  of  bodies  as  there  is  in  their  capacities  for  caloric;  that  in  compounds, 
therefore,  the  bodies  which  are  combined  are  negative  and  positive  in  their 
relationship  to  each  other,  and  that  they  will  consequently  be  attracted  to- 
wards the  opposite  poles  of  the  battery.  This  attraction  may  be  made  more 
powerful  than  chemical  affinity,  and  hence  it  follows  that  when  a  compound 
is  placed  in  the  electric  circuit,  its  constituents  will  be  separated,  one  por- 
tion going  over  to  the  negative,  and  the  other  to  the  positive  pole(44).  The 
particular  manner  of  proceeding  will  hereafter  be  shown  to  you;  but  we 


38.  What  circumstance  seems  to  militate  against  this  identity? 

39.  What  is  urged  in  reply  to  this  objection? 

40.  Is  the  shock  increased  by  enlarging  the  plates? 

41.  What  effect  is  produced  by  such  enlargement? 

42.  What  reason  is  given  for  this  increased  power  of  combustion? 

43.  What  is  Dr  Hare's  theory,  and  what  instrument  has  he  invented? 

44.  How  does  the  voltaic  battery  overcome  affinity? 


104  CONVERSATIONS  ON  CHEMISTRY. 

must  wait  until  we  arrive  at  the  substances  to  be  acted  upon,  in  the  regular 
progress  of  our  studies. 

I  might  describe  to  you  several  modes  of  constructing  the  voltaic  battery  > 
but  must  leave  them  as  objects  of  inquiry  for  yourselves  hereafter.  I  shall 
not  however  dismiss  the  subject  without  some  notice  of  the  remarkable  dis- 
coveries which  have  been  recently  made  respecting  the  intimate  connexion 
which  exists  between  electricity,  heat,  and  magnetism, — discoveries  which 
go  far  towards  justifying  the  opinion  that  they,  and  probable  light  also,  are 
all  modifications  of  the  same  etherial  matter,  and  have  even  been  thought  to 
9  promise  some  insight  into  the  nature  of  the  planetary  motions  them- 
selves(45). 

Caroline.  That  will  be  delightful.  We  may  then  make  little  worlds,  and 
set  them  revolving  round  each  other.  I  am  impatient  until  Iknow  how  this 
may  be  done. 

,  Mrs  B.  I  hope,  my  dear,  that  your  impatience  may  not  continue  until 
you  acquire  this  information,  or  I  fear  that  it  will  be  permanent.  This  is  a 
mere  speculation  of  some  warmly  imaginative  philosophers,  who  have  re- 
lated their  waking  dreams.  At  present  I  can  only  narrate  a  few  facts  to  you, 
and  exhibit  two  or  three  very  curious  experiments,  with  respect  to  which  I 
have  not  a  word  of  theory  to  offer,  and  shall  make  no  conjectures.  It  is  a 
subject  which  engages  the  attention  of  the  most  scientific  men,  from  whose 
united  labours  important  discoveries  may  be  reasonably  expected. 

Emily.  Then  we  must  be  content  to  be  observers  only,  and  not  inquirers . 
I  will  endeavour  to  play  my  part  well;  what  say  you  Caroline? 

Caroline.  I  well  know  that  I  shall  find  it  necessary  to  use  the  curb,  and 
shall  very  willingly  put  it  on.  The  lessons  which  I  have  received  have  not 
been  entirely  lost  upo*i  me?  for  although  I  like  as  well  as  ever  to  learn  how 
certain  effects  are  produced,  I  perceive  most  plainly  that  all  valuable  infor- 
mation of  this  kind  must  be  derived  from  observing  and  comparing  together 
a  great  number  of  facts.  It  would  be  extremely  unreasonable,  therefore,  to 
expect  a  satisfactory  theory  respecting  any  new  phenomenon  before  time  haa 
been  allowed  to  investigate  it  thoroughly.  The  world  had  existed  for  thou- 
sands of  years,  and  the  effects  of  gravitation  had  been  witnessed  by  every 
one,  yet  the  discovery  of  it,  as  pervading  the  universe,  was  reserved  for 
Newton. 

Mrs  B.  The  name  of  Electro-Magnetism  has  been  given  to  this  new 
branch  of  inquiry.  The  terms  thermo-magnetism  and  thermo-electricity  are 
also  applied  to  some  of  the  phenomena,  according  to  the  powers  which  ap- 
pear to  be  principally  engaged  in  or  developed  by  them(46). 

When  the  poles  of  a  voltaic  battery  are  connected  by  a  wire  extending 
from  one  to  the  other,  an  uninterrupted  current  of  the  fluid  passes  through 
it.  If  a  magnetic  needle  be  placed  near  this  connecting  wire,  it  will  be  made 
to  deviate  from  its  natural  position,  and  to  point  in  various  directions,  ac- 
cording to  the  mode  of  conducting  the  experiment;  thus  it  may  be  made  to 
point  east  and  ivest,  instead  of  north  and  south.  The  connecting  wire  is 
ane  of  platismm,  a  metal  not  oxidized  by  the  electric  current,  nor,  under 
ordinary  circumstances,  affected  by  the  magnet(47).  After  this  apparent 
attraction  had  been  discovered,  it  was  soon  ascertained  that  the  action  of 
the  connecting  wire  upon  the  magnet  was  not  owing  to  a  mere  attraction  ex- 
isting between  them,  but  to  a  tendency  which  they  have  to  revolve  round 
each  other(48). 


45.  What  is  said  respecting  the  imponderable  agents? 

46.  What  new  terms  are  employed  to  designate  their  action? 

47.  What  peculiar  action  exists  between  the  voltaic  battery  and  a  magnet? 

48.  What  is  the  tendency  of  the  magnet  and  of  the  wire? 


ON  VOLTAIC  ELECTRICITY.  105 

Caroline.  I  think,  Mrs  B. ,  that  the  accounts  which  have  appeared  of  the 
magnetism  of  a  compass-needle  on  board  a  ship  having  been  reversed  by  a 
stroke  of  lightning,  show  that  there  is  an  intimate  connexion  between  these 
two  powers. 

Mrs  JB.  There  are  several  such  accounts.  Needles  have  had  their 
poles  reversed,  their  magnetism  sometimes  destroyed,  and  at  others  com- 
municated by  lightning,  and  the  same  has  been  done  both  by  common  and 
voltaic  electricity(49). 

This  little  instrument  will  exhibit  the  rotatory  motion  of  a  wire  round  the 
pole  of  a  magnet.  A  cup  is  made  of  two  cylinders  of  sheet  copper;  the 
outer  one  about  two  inches  in  diameter,  and  the  inner  about  one  inch.  These 
have  a  bottom  by  which  they  are  connected  together,  but  which  does  not 
cross  the  inner  cylinder,  that  being  open  below  as  well  as  above.  This 
forms  a  cup  for  containing  a  diluted  acid  between  the  two  cylinders.  To  the 
inner  cylinder  a  copper  wire  is  soldered,  which  forms  a  bail  connecting  the 
opposite  sides.  From  the  centre  of  this  bail  a  point  projects  downwards, 
upon  which  it  can  freely  turn  upon  one  of  the  poles  of  a  strong  magnet.  A 
second  cylinder  or  tube  of  sheet  zinc,  about  one  inch  and  a  half  in  diameter, 

Instrument  for  Electro-magnetic  Section  of  the  Electro-magnetic 

rotation.  instrument. 


[c,  wire  supporting  the  tube  of  zinc. 
by  the  copper  vessel,  supported  by 
the  wire  a.  d,  the  magnet  passing 
through  the  inner  cylinder  of  the 
copper  vessel.] 


and  left  open  at  both  ends,  is  suspended  by  a  similar  bail,  as  you  see;  its 
point  resting  in  a  small  hollow  in  the  first  wire.  This  cylinder  of  zinc 
hangs  within  the  copper  cup  without  touching  it,  and  with  the  surrounding 
copper,  and  the  contained  fluid  forms  a  galvanic  arrangement.  The  cups 
being  suspended  upon  fine  points,  revolve  with  but  little  friction(SO).. 

Emily.  Astonishing!  they  both  begin  to  revolve,  but  turn  in  reversed 
directions.  I  do  not  wonder  that  a  fact  so  extraordinary  should  for  awhile 
puzzle  the  philosophers.  But  would  not  the  cups  revolve  without  the  mag- 
net, by  the  galvanic  influence  merely  ? 


49.  How  has  this  magnetism  of  a  needle  been  reversed  or  destroyed? 

50.  Can  you  describe  the  electro-magnetic  instrument? 


106 


CONVERSATIONS  ON  CHEMISTRY. 


Mrs  B.  Not  at  all;  it  is  the  combined  influence  of 
the  two  which  produces  the  result(51).  I  will  now 
show  you  a  similar  effect  without  the  voltaic  cups,  their 
absence  being  compensated  by  the  influence  of  caloric. 
This  apparatus  is  thence  denominated  therms-magnetic. 
These  little  wire  cages  are  formed  in  part  of  silver  and 
in  part  of  platinum;  they  have  each  a  point  by  -which 
I  suspend  them  upon  the  ends  of  this  horse-shoe  mag- 
net, so  that  one  surrounds  each  pole. 

When  the  spirit  lamp  below  is  lighted  the  cages  be- 
come heated,  and  immediately  begin  to  revolve,  in  con- 
trary directions,  and  this  they  will  continue  to  do  as 
long  as  the  lamp  is  allowed  to  burn.  We  have  here 
the  combined  action  of  magnetism,  heat,  and  electri- 
city; the  latter  being  undoubtedly  developed  by  the  ac- 
tion of  the  compound  metallic  cages. 

Caroline.  I  must  not  ask  any  thing  about  causes, 
and  I  am  sure  that  I  cannot  tell  any  thing  about  them; 
but  certainly  this  does  appear  like  a  peep  behind  the 
curtain  which  conceals  the  grand  arcana  of  nature,  and 
I  hope  to  live  long  enough  to  obtain  a  morp  perfect 
view(52). 

Mrs  B.  We  shall  at  our  next  conversation  proceed 
to  the  consideration  of  more  tangible  materials,  and  to 
matters  less  abstruse  than  those  which  we  have  had 
upon  the  tapis  to  day.  I  have  said  more  upon  the 
subject  of  electricity  than  I  at  first  intended;  but  it  has 
become  so  completely  interwoven  with  the  phenome- 
na of  chemistry,  that  we  can  scarcely  stir  a  step  with- 
out its  aid,  as  we  witness  its  influence  in  almost  every 
chemical  change,  whether  natural  or  artificial. 


Thermo-magnetic 

apparatus. 
A  A 


[A,  A,  wire  cages  of 
platinum  and  sil- 
ver, which  revolve 
in  opposite  direc- 
tions upon  the  two 
poles  of  the  mag- 
net when  the  lamg 
is  lighted.] 


CONVERSATION  X. 

ON    ATMOSPHERIC   AIR,    OXYGEN*,-  NITROGEN,  OR  AZOTE, 
AND  COMBUSTION. 

Constitution  of  Atmospheric  Mr.  Simple  Gases.  Vapours.  Distinctive 
Properties  of  Oxygen  and  Nitrogen.  Combustion  of  a  Candle  in  Atmos- 
pheric Jlir.  Lavoisierian  Theory  of  Combustion.  Its  defects.  Fixed  and 
Volatile  Products.  Oxygen  discovered  by  Priestley.  How  obtained. 
Pneumatic  Cistern. 

Mrs  B.  To  day  we  shall  examine  the  chemical  properties  of  the  atmos- 
phere, and  of  the  two  simple  gases  of  which  it  is  composed. 

Emily.  I  always  thought  that  the  atmosphere  was  a  very  complicated 
fluid,  composed  of  all  the  variety  of  exhalations  from  the  earth. 

Mrs  B.  These  various  exhalations  are  contained  in  the  atmosphere,  but 
must  be  considered  as  accidental  mixtures,  like  the  heterogeneous  substan- 
ces dissolved  in  water,  which  fluid  we  never  find  in  a  state  of  absolute  purity. 


51.  How  do  the  eups  revolve,  and  what  proves  the  action  of  two  powers? 

52.  Will  you  describe  the  thermo-magnetic  apparatus? 


ON"  ATMOSPHERIC  AIR.  107 

The  essential  ingredients  of  the  atmosphere  are  OXYGEN  GAS  and  KITBOGEIT 
GAS,  or  azote(l). 

Emily.     Pray  tell  me  in  what  respect  air  and  gas  differ  from  each  other? 

•Mrs  B.  Strictly  speaking  they  are  synonymous  terms,  hut  in  common 
language  when  we  speak  of  air  we  mean  the  atmosphere,  no  other  species  of 
air  having  been  formerly  known.  When  the  airs  were  found  to  be  nume- 
rous, the  term  gas  was  adopted  as  a  generic  one.  Any  fluid  which  remains 
permanently  elastic  under  atmospheric  pressure,  at  every  natural  tempera- 
ture, is  called  a  gas(2).  Oxygen,  nitrogen,  and  some  others  are  sometimes 
called  simple  gases,  because  they  contain  but  one  base,  there  being  some 
gases  which  have  two  or  more  bases(3). 

Caroline.  I  do  not  understand  this  acceptation  of  the  term  base.  If  a  gas 
is  simple,  it  must  consist  of  one  material  only. 

J\frs  B.  By  a  base  -we  mean  the  principal  ponderable  material  -which  en- 
ters into  the  composition  of  a  body,  and  upon  -which  its  characteristic  proper* 
ties  depend(k).  The  term  gas  at  once  indicates  the  presence  of  caloric,  as 
necessarily  as  do  the  words  steam  and  vapour.  Oxygen  gas  is  a  combina- 
tion of  oxygen  with  caloric,  and  nitrogen  gas  of  nitrogen  and  caloric.  Oxy- 
gen is  the  base  in  one  case,  and  nitrogen  in  the  other(5). 

Emily.  Then  the  only  difference  between  a  vapour  and  a  gas  would  ap- 
pear to  be  the  temperature  at  which  they  are  converted  into  liquids  or  into 
solids(6). 

JWrs  B.  Precisely  so,  and  many  of  them  have  actually  been  rendered 
liquid  by  the  united  influence  of  cold  and  of  great  mechanical  pressure.  It 
appears  perfectly  fair,  therefore,  to  consider  the  gases  as  being  the  vapours  of 
liquids  which  are  so  volatile  that  their  boiling  point  under  atmospheric  pres- 
sure is  lower  than  any  natural  temperature(7).  You  must  therefore  never 
expect  to  see  the  b&ses  of  these  gases  in  their  simple  state;  for  when  disen- 
gaged from  any  solid  in  which  they  are  combined,  they  instantaneously  be- 
come gases;  because  there  is  no  natural  reduction  of  temperature  at  which 
they  do  not  find  caloric  enough  to  convert  them  into  that  form(8). 

Caroline.  In  what  proportions  are  the  two  gases  contained  in  the  atmos- 
phere? 

Mrs  B.  The  oxygen  gas  is  generally  estimated  at  a  little  more  than  one 
fifth.  One  hundred  parts  by  measure  of  atmospheric  air  have  been  said  to 
contain  twenty-one  measures  of  oxygen  and  seventy-nine  of  nitrogen.  Some 
eminent  chemists,  however,  think  that  twenty  of  the  one  to  eighty  of  the 
other  may  safely  be  set  down  as  the  true  proportions(9). 

When  separated  from  each  other,  as  you  have  already  been  informed, 
their  qualities  are  found  to  be  totally  different.  The  nitrogen  will  not  sup- 
port combustion  or  animal  life,  whilst  in  the  oxygen  every  combustible  burns 
with  greatly  increased  splendor  and  rapidity.  Animals  also  will  live  longer 
in  a  confined  portion  of  it  than  in  the  same  bulk  of  atmospheric  air,  and 
for  a  time,  appear  to  experience  a  pleasant  stimulus(lO) 

Caroline.     What  a  pity  that  there  should  be  but  one-fifth  of  oxygen  in 


1.  Of  what  does  the  air  of  the  atmosphere  consist? 

2.  What  do  we  intend  by  the  terms  air  and  gas? 

3.  When  are  airs  or  gases  denominated  simple? 

4.  What  is  meant  by  the  term  base? 

5.  What  does  the  term  gas  indicate,  and  what  are  its  examples? 

6.  In  what  do  vapours  and  gases  differ  from  each  other? 

7.  What  proof  is  adduced  of  the  analogy  between  them? 

8.  What  is  the  difficulty  in  procuring  the  bases  of  the  gases? 

9.  In  what  proportion  are  the  two  gases  contained  in  the  atmosphere? 
10.  How  are  oxygen  and  nitrogen  distinguished  when  separate? 


108  CONVERSATIONS  ON  CHEMISTRY. 

the  air.  If  the  proportion  was  greater  our  candles  would  give  more  light) 
our  fires  more  heat,  and  we  should  probably  breathe  more  freely,  and  live 
more  merrily  than  we  now  do.  If  the  nitrogen  neither  supports  life  nor 
combustion,  I  do  not  see  its  use. 

Jlfrs  B.  And  probably  you  never  will  know  one-half  of  its  uses.  But 
He  who  formed  the  atmosphere,  has  in  infinite  wisdom  adapted  it  to  the  per- 
fect fulfilment  of  his  beneficent  designs.  In  pure  oxygen  your  candle  would 
disappear  in  a  minute  or  two,  and  even  your  iron  candlesticks  would  take 
fire  and  burn  up;  and  it  would  be  just  as  rational  to  desire  our  rivers  and 
springs  to  flow  with  brandy,  as  to  wish  for  an  atmosphere  of  pure  oxygen, 
the  stimulating  effects  of  which  would  rapidly  destroy  life(ll). 

That  the  nitrogen  contained  in  the  atmosphere  is  as  necessary  to  living 
animals  as  the  oxygen,  will  appear  plain  to  you,  when  I  inform  you  that  it 
has  been  ascertained  that  their  well-being  not  only  depends  upon  its  pre- 
sence, but  upon  its  being  present  in  the  exact  proportion  in  which  we 
find  it(12). 

Emily.  And  by  what  means  can  the  two  gases  which  compose  the  atmos- 
phere be  separated,  so  that  we  may  examine  their  properties. 

JMrs  J8.     There  are  many  ways  of  effect- 
ing their  separation,  and  of  obtaining  the  ni-   Candle  burnt  in    atmospheric 
trogen  gas,  but  we  know  of  no  process  by  air  under  a  receiver. 

which  to  separate  the  nitrogen  and  leave  the 
oxygen  in  the  gaseous  form(13).  A  burning 
body  placed  in  a  confined  portion  of  atmos- 
pheric air  will  cause  its  decomposition.  I 
place  this  lighted  candle  under  a  bell  glass, 
the  bottom  of  which  stands  in  water;  it  im- 
mediately burns  dimly,  and  is  now  extin- 
guished. The  larger  portion  of  the  oxygen 
has  disappeared,  and  a  second  candle  placed 
in  the  air  which  remains,  would  go  out  in- 
stantaneously. A  portion  of  the  water  you 
see  rises  into  the  glass:  this  isin  consequence 
of  the  absorption  of  the  oxygen  leaving  a 

void  space,  and  the  pressure  of  the  atmosphere  forcing  the  water  up  to  oc- 
cupy it(!4). 

Caroline.  How  surprising  that  a  burning  candle  should  decompose  the 
atmosphere  and  absorb  its  oxygen.  The  water  I  suppose  will  rise  so  as  to 
occupy  one-fifth  of  the  contents  of  the  glass. 

JUrs  B.  Not  so;  the  whole  of  the  oxygen  is  not  separated,  although  there 
is  too  little  left  to  support  combustion;  and  besides  this  there  is  another  gas, 
produced  in  the  burning,  which  occupies  a  part  of  the  space  formerly  filled 
by  the  oxygen(15).  There  are,  however,  some  combustibles  which  will  unite 
to  the  whole  of  the  oxygen  and  convert  it  into  the  solid  form:  the  nitrogen 
will  in  this  case  be  left  in  a  state  of  purity.  That  the  atmosphere  should  be 
decomposed  by  combustion  is  no  more  wonderful  than  that  the  candle  should 
be  so  also.  The  tallow  which  disappears  must  combine  with  something, 
and  in  the  present  instance  that  something  is  oxygen(16). 

Emily.     Although  I  knew  that  air  was  necessary  to  combustion,  I  never 


11.  What  would  take  place  in  an  atmosphere  of  pure  oxygen? 

12.  What  other  fact  evinces  the  use  of  the  nitrogen? 

13.  Can  the  two  gases  be  separated,  so  as  to  obtain  either  at  pleasure? 

14.  How  may  the  oxygen  be  separated  by  means  of  a  candle? 

15.  Why  will  not  the  nitrogen  be  left  pure? 

16.  What  remarks  are  made  respecting  this  decomposition? 


ON  ATMOSPHERIC  AIR,  AND  COMBUSTION.  109 

had  an  idea  of  the  importance  of  its  agency  until  now,  but  it  is  evidently  as 
necessary  to  the  process  as  the  fuel  itself. 

Mrs  B.  We  are  indebted  to  that  eminent  French  chemist  Lavoisier  and 
his  associates  for  what  is  called  the  modern  theory  of  chemistry,  and  also 
for  the  nomenclature,  or  system  of  names,  which  is  now  employed  by  chem- 
ists(17).  Lavoisier's  theory  of  combustion  was  also  generally  adopted,  and 
deemed  satisfactory.  It  taught  that  combustion  consisted  in  the  rapid  combi- 
nation of  oxygen  -with  a  'combustible  body,  and  the  consequent  disengagement 
of  heat  and  tight(\%). 

Caroline.  How  simple,  and  how  beautiful!  How  perfectly  it  accords 
with  what  we  have  seen!  But  pray  whence  do  the  light  and  heat  come  ? 

Mrs  B.  That  is  a  question  which  in  some  instances  maybe  satisfactorily 
answered,  but  there  are  others  ia  which  the  theory  fails  in  accounting  for 
the  production  of  heat;  and  therefore,  notwithstanding  its  simplicity  and  its 
beauty,  it  is,  like  most  other  theories,  imperfect(19). 

It  has  been  believed  that  light  is  a  constituent  both  of  gaseous  and  of  com- 
bustible bodies,  and  that,  in  their  combination,  a  portion  of  it  is  given  out. 
Caloric,  also,  is  a  constituent  of  gaseous  bodies,  and  consequently  of  oxygen, 
and  has  been  supposed  to  supply  the  heat  which  is  disengaged  in  combus- 
tion(20).  Oxygen  frequently  combines  with  the  combustible  and  passes  into 
the  solid  or  liquid  state,  and  of  course  gives  out  the  caloric  which  converted 
it  into  a  gas(21 ).  At  other  times  it  combines  with  the  combustible  and  forms 
•with  it  a  compound  gas,  the  capacity  of  which  for  caloric  is  less  than  that  of 
oxygen,  and,  of  course,  latent  heat  will  then  be  rendered  sensible;  and  that 
in  a  degree  proportioned  to  this  difference  of  capacity(22). 

Caroline.  But  this  would  be  to  suppose  that  the  heat  came  from  the  air 
and  not  from  the  fuel,  which  seems  contrary  to  our  experience. 

Mrs  B.  Recollect,  my  dear,  that  our  conversations  need  not  be  continu- 
ed, if  your  senses  alone  are  to  be  your  guides.  In  the  slaking  of  lime  you 
now  believe  that  the  heat  disengaged  is  derived  from  the  water;  and  when 
you  are  convinced  that  oxygen  gas  is  as  necessary,  and  as  actively  engaged 
in  the  process  of  combustion  as  the  fuel  itself,  you  must  be  compelled  to  at- 
tribute to  it  a  full  share  in  producing  the  effect,  although  it  is  itself  invisible. 

The  combination  takes  place  only  at  the  surface  of  the  burning  body,  where 
the  air  has  free  access  to  it(23).  ^ 

Emily.  What  are  the  principal  objections  to  the  Lavoisierian  theory  or 
combustion? 

Mrs  B.  At  the  time  the  theory  was  proposed,  oxygen  was  the  only 
known  supporter  of  combustion,  but  there  are  other  agents  which  are  now 
admitted  into  the  class:  these  are  chlorine,  iodine,  and  perhaps  bromine. 
Although  combustion  does,  in  general,  consist  in  the  rapid  combination  of 
oxygen  with  a  combustible  body,  this  is  not  universally  the  case(24). 

There  are  also  many  chemical  combinations  which  are  accompanied  by 
the  disengagement  of  light  and  heat,  where  neither  of  these  supporters,  as 
they  have  been  called,  are  present(25).  In  many  instances  of  combustion  we" 


17.  Who  were  the  authors  of  the  modern  theory  and  nomenclature? 

18.  What  definition  did  Lavoisier  give  of  combustion? 

19.  Why  is  this  theory  accounted  imperfect? 

20.  Whence  have  the  light  and  heat  been  supposed  to  be  derived? 

21.  What  change  in  the  oxygen  may  cause  it  to  give  out  heat? 

22.  When  the  product  is  a  gas,  whence  may  the  heat  be  derived? 

23.  What  observations  are  made  respecting  oxygen  being  the  source  of 
heat? 

24.  What  objections  exist  against  the  theory  of  Lavoisier? 

25.  What  further  objection  is  stated? 

K 


110  CONVERSATIONS  ON  CHEMISTRY. 

are  not  acquainted  with  the  source  of  the  heat,  as  in  the  firing  of  gunpowder, 
and  other  explosive  mixtures.  In  these,  solids  are  converted  into  gases,  and 
this,  according  to  the  Lavoiserian  theory,  should  produce  cold,  as  an  increased 
capacity  for  calorie  is  the  necessary  result  of  such  a  change(26).  It  is  now, 
therefore,  the  practice  among  chemists  to  state,  in  general  terms,  that  combus- 
tion is  the  result  of  energetic  chemical  action^?). 

In  our  present  conversation,  when  speaking  of  combustion,  you  are  to  un- 
derstand me  as  intending  the  burning  of  bodies  in  atmospheric  air,  oxygen  gas, 
or  some  gas  containing  oxygen;  and  the  products  of  combustion  as  consisting 
of  a  combination  of  oxygen  with  the  combustible  body(28).  The  exceptions 
we  shall  place  by  themselves,  as  they  are  instances  of  combustion  with  which 
you  are  not  familiar. 

Emily.  By  the  products  of  combustion,  I  suppose  you  mean  the  smoke 
and  ashes,  or  other  substances  which  are  left  after  a  body  has  been 
burned. 

Mrs  B.  This  would  be  not  only  a  very  meagre,  but  a  very  incorrect 
definition.  In  the  greater  number  of  instances  the  products  of  combustion 
exist  in  the  gaseous  form,  and  are  from  this  cause  invisible;  they  are  then 
called  volatile  products.  When  they  remain  in  the  solid  state,  they  are  called 
fixed prodiicts(2V}.  The  whole  of  the  tallow  of  our  candles,  and  of  the  oil  of 
our  lamps,  and  a  large  proportion  of  our  wood  and  coals  form,  with  the  oxy- 
gen, volatile  products,  which,  if  collected  and  weighed,  will  be  found  to 
contain  all  the  matter  that  has  apparently  vanished,  not  an  atom  being 
lost(30).  Smoke  is  not  properly  a  product  of  combustion,  as  it  consists 
principally  of  a  part  of  the  fuel  which  escapes  combustion,  and  which,  by  its 
condensation,  forms  the  soot  in  our  chimneys(Sl). 

When  the  products  of  combustion  are  altogether  of  the  kind  called  fixed, 
it  is  easy  to  show  that,  in  burning,  they  have  acquired  weight,  instead  of 
suffering  a  diminution. 

Emily.  That  is  very  extraordinary;  for  although  the  light  and  heat  which 
have  escaped  may  weigh  nothing,  and  the  body  may  not  sensibly  lose  weight, 
it  is  strange  that  it  should  become  heavier. 

Caroline.  It  has  just  occurred  to  me  how  this  may  be;  you  know  that  the 
air  possesses  weight,  and  if  the  oxygen  gas  unites  with  the  combustible,  the 
two  together  must  weigh  more  than  the  one(32). 

.Mrs  B.  You  have  given  the  correct  explanation,  and  yet  have  made  one 
mistake:  the  oxygen,  which  is  the  base  of  the  oxygen  gas,  combines  with  the 
combustible,  assumes  the  solid  form,  and  loses  its  existence  as  a  gas.  You 
must  carefully  distinguish  between  a  gas  and  its  base,  or  your  ideas  upon 
this  subject,  like  those  of  many  others,  will  be  frequently  confused(33). 

Caroline.  Combustibles,  I  know,  are  bodies  which  may  be  burned;  pro- 
ducts of  combustion  I  understand  to  be  those  which  have  been  burned;  but 
there  are  many  which  do  not  belong  to  either  of  these  classes,  such  as  rocks, 
earths,  metals,  and,  I  think,  a  great  many  others(34). 

Mrs  B.  A  little  time  will  teach  you  that  the  bodies  which  you  have 
named  are  either  combustibles,  or  products  of  combustion.  Rocks  and 


26.  How  does  the  firing  of  gunpowder,  &c.  militate  against  it? 

27.  What  more  general  definition  may  be  given  of  combustion? 

28.  How  are  we  at  present  to  limit  the  remarks  on  this  process? 

29.  How  are  the  products  of  combustion  divided,  and  why? 

30.  What  is  said  of  the  products  from  tallow,  oil,  coals,  &c.? 

31.  Is  smoke,  properly  speaking,  a  product  of  combustion? 

32.  What  do  we  find  the  fixed  products  to  have  acquired,  and  why? 

33.  Does  the  gas  combine  with  the  combustible  body? 

34.  What  does  Caroline  remark  respecting  combustible  products,  &c 


f 


ON  ATMOSPHERIC  AIR,  AND  COMBUSTION.  Ill 

earths  are  generally  compounds  of  a  combustible  body  with  oxygen,  and  the 
metals  are  all  combustible,  notwithstanding  some  of  them  require  a  most 
intense  heat  to  cause  them  to  burn.  Some  bodies,  you  know,  take  fire  at  a 
much  lower  temperature  than  others(35). 

Emily.  But  are  there  not  some  combustibles  which  have  so  strong  an 
attraction  for  oxygen,  that  they  will  rapidly  combine  with  it  Without  first 
applying  heat  to  them? 

Caroline.  That  cannot  be,  otherwise  we  should  see  such  bodies  taking 
fire  and  burning  spontaneously. 

Mrs  B.  There  are  in  existence  some  such  bodies,  such  as  phosphorus, 
potassium,  and  others,  with  which  you  will  hereafter  become  acquainted. 
These  bodies,  however,  are  all  prepared  by  art;  as,  naturally,  they  are  found 
combined  with  oxygen,  from  which  it  is  necessary  to  separate  them  by  che- 
mical means.  -  The  very  nature  of  such  bodies  forbids  their  existing  in  an 
uncombined  state  any  where  near  the  surface  of  the  earth,  where  oxygen  can 
have  access  to  them(36). 

Emily.     Was  not  oxygen  gas  discovered  by  Lavoisier? 

Mrs  B.  No,  my  dear,  it  was  discovered  in  the  year  1774  by  Dr  Priest- 
ley, who  called  it  dephlogisticated  air.  It  afterwards  received  the  name  of 
vital  air,  because  it  is  necessary  to  the  support  of  life,  and  Lavoisier  called 
it  OXYGEN,  a  name  derived  from  two  Greek  words,  signifying  acid,  and  to 
generate;  because  it  was  found  that  many  combustibles  in  their  combination 
with  oxygen  were  converted  into  acids(37).  Thus  sulphuric  acid,  or  oil  of 
vitriol,  is  produced  by  the  combination  of  oxygen  with  sulphur.  Oxygen 
was  believed,  therefore,  to  be  the  acidifying  principle,  and  it  was  assumed 
that  all  the  acids  contained  it(38).  We  have  since  learned  that  it  is  not  the 
only  supporter  of  combustion,  and  have  also  discovered  that  some  acids 
exist  which  do  not  contain  it(59). 

Caroline.  I  long  now  to  see  some  of  the  rapid  and  brilliant  combustions 
which  take  place  in  oxygen  gas.  Is  it  difficult  to  procure  it  in  a  state  of 
purity  ? 

Mrs  B.  It  is  not  difficult  to  procure  it  sufficiently  pure  to  exhibit  its 
properties;  but  to  obtain  any  chemical  agent  absolutely  pure  is  a  task  rarely 
accomplished,  and  fortunately  not  often  necessary(40).  Oxygen  is  so  feebly 
combined  with  some  of  the  metals,  that  heat  alone  will  separate  it,  and  con- 
vert it  into  a  gas(4l).  It  was  from  red  precipitate  that  Dr  Priestley  first 
obtained  it.  Red  precipitate,  or  red  oxide  of  mercury,  as  it  was  afterwards 
called,  consists  of  oxygen  united  to  quicksilver;  and  in  order  to  separate  them, 
it  is  sufficient  to  heat  the  compound,  when  the  oxygen  unites  to  caloric  and 
becomes  a  gas,  and  the  mercury  is  reduced,  or  brought  back  again  into  the 
state  of  quicksilver(42).  Red  lead,  or  red  oxide  of  lead,  and  black  oxide 
of  manganese,  in  the  former  of  which  oxygen  is  combined  with  lead,  and 
in  the  latter  with  a  metal  called  manganese,  give  out  this  gas  when  heated 
to  redness  in  a  retort  of  iron  or  of  earthenware(43).  When  this  last  oxide  is 
mixed  with  sulphuric  acid,  oxygen  is  separated  from  it  by  a  very  moderate 


35.  What  is  said  of  the  nature  of  earths  and  stones,  and  of  metals? 

36.  What  kind  of  combustibles  must  we  obtain  by  art,  and  why? 

37.  Who  discovered  oxygen,  who  so  named  it,  and  why? 

38.  What  acid  is  mentioned  as  an  example? 

39.  Why  is  it  not  still  accounted  the  acidifying  principle? 

40.  What  is  remarked  respecting  obtaining  articles  perfectly  pure? 

41.  What  is  the  fact  respecting  oxygen  and  certain  metals? 

42.  From  what  was  it  first  obtained,  and  how? 

43.  What  substances  yield  oxygen  gas  when  heated  red  hot? 


112 


CONVERSATIONS  ON  CHEMISTRY. 


heat,  as  by  that  of  a  lamp(44).  Common  nitre,  or  saltpetre,  also  contains  a 
large  quantity  of  oxygen,  with  which  it  parts  readily,  as  do  some  other  sub- 
stances; so  that  we  have  various  methods  of  procuring  it. 

I  have  put  into  this  retort  some'  pulverized  black  oxide  of  manganese, 
and  poured  upon  it  enough  sulphuric  acid  to  form  a  sort  of  paste.  The 
joint  action  of  this  acid,  and  of  the  heat  from  a  lamp,  will  suffice  to  tlisen- 
gage  a  portion  of  the  oxygen,  and  convert  it  into  the  gaseous  state(45). 

Emily.  I  am  at  a  loss  to  know  in  what  manner  you  can  collect  it,  and 
keep  it  from  mixing  with  common  air;  although  I  have  no  doubt  you  have 
some  ingenious  device  for  effecting  this. 

•Mrs  JB.  The  means  are  very  simple  and  very  perfect.  Before  the  time 
of  Priestley,  chemists  knew  but  little  of  the  gases.  From  his  numerous  dis- 
coveries, this  philosopher  has  been  emphatically  styled  the  father  of  pneu- 
matic chemistry;  for  although  some  of  the  gases  had  been  distinctly  noticed 
by  others,  the  greater  number  were  made  known  by  his  researches.  To  him 
also  we  are  indebted  for  a  most  convenient  mode  of  collecting  them. 

Pneumatic  cistern,  -with  a  bell  glass  upon  a  shelf  under  water;  a  retort  from 
-which  gas  is  passing  into  the  receiver;  and  a  lamp  for  heating  the  materials 
in  the  retort. 


This  vessel,  which  I  am  about  to  use,  is  called  the  pneumatic  cistern,  or 
tub.  It  has  a  shelf  within  it,  at  about  two  inches  below  its  upper  edge. 
Water  is  poured  into  it  so  as  to  cover  the  shelf  completely.  Through  this 
shelf,  holes  are  made  for  the  passage  of  gas,  the  lower  side  around  each  hole 
being  scooped  out  so  as  to  form  in  the  wood  a  sort  of  inverted  funnel,  to  col- 
lect and  conduct  the  gas.  A  receiver  called  a  bell  glass,  a  tumbler,  phial, 
or  other  vessel  is  filled  with  water,  and  placed  with  its  open  mouth  over  one 
of  the  holes  in  the  shelf(46).  If  now  the  beak  of  a  retort,  or  a  tube  from 
any  vessel  from  which  gas  is  to  proceed,  be  made  to  pass  under  the  shelf,  the 
bubbles  of  air  will  ascend  through  the  water,  and  gradually  displace  that  in 
the  glass  vessel;  and  as  the  water  had  excluded  the  atmospheric  air  from  it, 


44.  How  may  it  be  obtained  at  a  moderate  heat? 

45.  Describe  the  preparatory  steps  of  the  pi-ocess. 

46.  Describe  the  pneumatic  cisternt  with  a  receiver  placed  on  it. 


ON  OXYGEN.  113 

the  gas  whicn  passes  up  will  be  collected,  uncontaminated  by  admixture  with 
any  other(47). 

Caroline.  How  beautiful  the  bubbles  appear  in  rising,  and  how  simple 
and  convenient  is  the  apparatus  altogether!  I  shall  be  delighted  to  make 
some  experiments  with  it  myself. 

Mrs  B.  You  can  try  your  skill  in  that  way  at  your  leisure;  but  as  you 
will  find  some  experience  necessary  in  order  to  manage  it  with  address,  it 
will  be  best  for  you  to  practice  at  first  with  atmospheric  air,  which  you  may 
pour  from  one  inverted  vessel  into  another,  as  I  shall  transfer  into  this  wide 
mouthed  phial  some  of  the  oxygen  which  we  are  now  collecting.  To  do 
this  I  fill  the  phial  with  water,  and  invert  it  over  one  of  the  holes  on  the 
shelf;  I  then  press  the  larger  vessel,  containing  the  oxygen,  sufficiently  deep 
in  the  water  to  pass  its  edge  under  the  shelf,  so  that  when  I  tilt  it  on  one 
side,  the  gas  which  escapes  from  it  shall  be  conducted  into  the  phial.  In. 
this  way  gases  can  be  poured  from  one  vessel  into  another  with  great  facil- 
ity(48). 

Emily.  But  it  is  an  unusual  kind  of  pouring,  upwards  instead  of  down- 
wards: this  however  must  necessarily  result  from  the  levity  of  the  gas(49). 
Now  you  have  filled  the  phial,  we  shall  have  the  pleasure  of  seeing  how  bril- 
liantly bodies  burn  in  oxygen. 

Mrs  B.  I  have,  ready  prepared,  a  sufficient  portion  of  the  gas  to  per- 
form this  and  other  experiments  illustrative  of  its  properties,  and  of  the 
nature  of  combustion  in  general.  Whilst  exhibiting  them  I  shall  take  the 
opportunity  of  explaining  such  parts  of  the  nomenclature  of  chemistry, 
as  are  immediately  connected  with  the  experiments.  This  is  a  subject 
which  will  claim  and  merit  your  undivided  attention;  and  although  I  keep 
you  on  the  tiptoe  of  expectation,  I  still  think  it  best  to  postpone  it  until 
our  next  meeting,  in  attending  which  1  need  not  invite  you  to  be  punctual. 


CONVERSATION  XI. 

ON  OXYGEN,  SOME   OF  ITS   COMBINATIONS,  AND   THE 
NAMES  GIVEN  TO  THEM. 

Combustion  of  a  Candle.  Of  Iron  Wire.  Oxides  and  Oxidation.  Acids 
and  Alkalies.  Names  of  Acids.  Tests  or  Reagents.  Decomposition  of 
the  Alkalies.  Neutralization.  Nomenclature  of  Oxides.  Of  Salts  and 
their  Bases.  Designation  of  Combining  Proportionals. 

Emily.  Here  we  are,  Mrs  B.,  waiting  for  you;  and  although  we  always 
derive  light  from  your  presence,  we  are  sure  that  an  unusual  brilliancy  will 
attend  you  in  your  appearance  to-day.  Should  the  light  which  you  will 
diffuse  prove  as  durable  as  it  will  be  splendid,  I  believe  that  we  shall 
never  again  have  to  complain  of  darkness. 

Mrs  B.  You  must  take  care,  however,  not  to  be  so  dazzled  by  the  light 
of  the  experiments  as  to  allow  your  vision  to  be  too  much  dimmed  to  dis- 
cover the  truths  which  they  are  designed  to  place  within  your  view.  The 
beautiful  objects  in  nature  are,  in  general,  best  seen  by  the  mild  reflected 


47.  How  is  the  gas  made  to  pass  into  such  a  receiver? 

48.  How  may  gases  be  poured  from  one  vessel  into  another? 

49.  In  what  direction  is  the  pouring,  and  why? 

K  2 

"•  ••  •  "  jf/  <-." 

V 


114 


CONVERSATIONS  ON  CHEMISTRY. 


[A  taper 
burnt     in 
oxygen 

gas.] 


light  of  the  sun,  and  the  analogy  will  hold  good  in  the  examination  of  the 
truths  of  science. 

Our  first  example  of  combustion  in  oxygen  gas  will  be  that 
of  a  taper,  which,  for  convenience  sake,  I  have  attached  to  a 
piece  of  bent  wire.  I  now  light  the  taper  and  introduce  it  into 
the  jar;  and  you  perceive  how  much  the  flame  is  increased,  both 
in  size  and  brilliancy.  If  I  blow  out  the  taper,  and  immerse  it 
again  in  the  gas  before  the  wick  is  entirely  extinguished,  it 
will  burst  into  a  flame  with  a  slight  explosion  ;  and  this  you 
perceive  I  can  repeat  five  or  six  times  in  succession(l). 

Caroline.  What  a  beautiful  experiment!  and  how  plainly 
it  shows  that  an  atmosphere  of  pure  oxygen  would  not  answer 
our  purposes,  although  it  might  make  good  business  for  the 
tallow-chandlers.  Our  candles  would  burn  away  as  fast  as  we. 
could  light  them,  and  it  would  be  of  no  use  to  blow  them  out, 
as  they  would  be  instantaneously  rekindled (2). 

•Mrs  B.  The  metals  I  have  told  you  are  combustibles,  and 
most  of  them  may  be  made  to  burn  very  readily  in  oxygen.  I  will  show 
you  the  experiment  of  burning  iron,  the  combustion  of  which  is  very  rapid 
and  brilliant. 

Emily.  It  is  well  that  iron  will  not  burn  in  atmospheric  air,  or  I  do  not 
know  of  what  we  should  make  our  grates  and  stoves. 

Mrs  B.  At  a  very  elevated  temperature,  iron  will  burn  in  atmospheric 
air,  as  the  blacksmith  sometimes  learns  to  his  cost,  when  he  leaves  it  too 
long  in  his  fire.  When  minutely  divided,  it  burns  very  readily,  as  you  will 
find  by  dropping  some  iron  filings  into  the  flame  of  a  candle(3). 

The  usual  way  of  burning  iron  in  oxygen 
gas  is  to  twist  a  piece  of  piano  forte  wire, 
spirally,  like  a  cork  screw.  One  end  of  this 
wire  is  fixed  into  a  cork  which  fits  the  top  of  a 
receiver,  and  around  the  other  end  a  small  piece 
of  thread  may  be  wound.  This  should  be 
touched  with  wax,  or  sulphur,  to  ignite  the 
wire  in  the  first  instance;  as  the  combus- 
tion cannot  commence  unless  the  wire 
be  red  hot(4).  This  receiver  is  filled  with 
oxygen,  and,  as  you  see,  has  its  lower  end 
standing  in  water.  I  will  now  light  the  piece 
of  thread  and  then  remove  the  stopper,  and 
insert  the  cork  in  its  place. 

Caroline.  Is  there  no  danger  of  the  gas 
escaping  while  you  change  the  stoppers? 

Jlfrs  B.  Oxygen  gas  is  a  little  heavier  than 
atmospheric  air!"  It  therefore  will\not  escape 
very  rapidly;  and  if  1  do  not  leave  the  opening 
uncovered,  we  shall  lose  but  a  very  small 
quantity (5). 

Caroline.  Oh,  what  a  brilliant  and  beauti- 
ful flame ! 

Emily.     It  is  almost   as   dazzling  as  the  sun. — Now   a   piece   of  the 


[Combustion  of  iron  wire 
in  oxygen  gas.] 


1.  How  is  the  burning  of  a  taper  in  oxygen  managed,  and  what  occurs? 

2.  What  would  be  the  result  in  an  atmosphere  of  pure  oxygen? 

3.  Under  what  circumstances  will  iron  burn  in  atmospheric  air? 

4.  How  should  iron  wire  be  prepared  to  burn  in  oxygen? 

5.  How  should  it  be  inserted  in  the  vessel? 


ON  OXYGEN.  115 

melted  wire  drops  to  the  bottom.  I  fear  it  is  extinguished;  but  no,  it  burns 
again  as  brightly  as  ever. 

JMrs  B.  It  will  burn  till  the  wire  is  entirely  consumed,  provided  the 
oxygen  is  not  first  exhausted;  for  you  know  it  can  burn  only  while  there  is 
oxygen  to  combine  with  it(6). 

Caroline.  I  never  saw  a  more  beautiful  light.  My  eyes  can  hardly  bear 
it.  How  astonishing  to  think  that  all  this  caloric  was  contained  in  the  small 
quantity  of  gas  and  iron  which  were  enclosed  in  the  receiver,  and  that  with- 
out producing  any  sensible  heat ! 

Emily.  How  wonderfully  quick  combustion  goes  on  in  pure  oxygen  gas! 
But  pray,  are  these  drops  of  burnt  iron  as  heavy  as  the  original  wire? 

Mrs  B.  They  are  even  heavier;  for  the  iron,  in  burning,  has  acquired 
exactly  the  weight  of  the  oxygen  which  has  disappeared  and  is  now  com- 
bined with  it.  It  has  become  an  oxide  of  iron(7). 

Caroline.  I  do  not  know  what  you  mean  by  saying  that  the  oxygen  has 
disappeared,  Mrs  B.,  for  it  was  always  invisible. 

•Mrs  B.  True,  my  dear,  the  expression  was  incorrect.  But  though  you 
could  not  see  the  oxygen  gas,  I  believe  you  had  no  doubt  of  its  presence,  as 
the  effect  it  produced  on  the  wire  was  sufficiently  evident. 

Caroline.  Yes,  indeed;  and  I  am  also  convinced  that  in  the  combustion, 
both  the  oxygen  and  the  iron  have  suffered  decomposition. 

Mrs  B.  You,  in  your  turn,  are  not  quite  correct.  Simple  bodies  cannot 
be  decomposed.  The  oxygen  and  iron  are  both  simple,  and  they  have  com- 
bined and  formed  a  compound,  which,  were  you  to  decompose  it,  would 
again  furnish  you  with  iron  and  with  oxygen(8).  The  oxygen  gas  is  decom- 
posed, and  the  whole  of  the  intense  heat  given  out  in  the  combustion,  is  pro- 
bably derived  from  it,  as  its  base  has  assumed  the  solid  form(9).  The  little 
globules  which  you  have  seen  fall  down,  and  which  are  the  product  of  this 
combustion,  are  an  oxide  of  iron,  and  will,  as  we  have  already  remarked, 
be  found  to  weigh  more  than  the  iron  did  before  its  combustion. 

Caroline.  I  wish  that  we  had  weighed  the  wire  and  the  oxygen  gas  be- 
fore the  combustion;  we  might  then  have  determined  whether  the  weight 
of  the  oxide  was  equal  to  that  of  both. 

Mrs  B.  You  may  try  the  experiment  if  you  particularly  wish  it;  but 
I  can  assure  you  that,  if  accurately  performed,  it  never  fails  to  show  that  the 
additional  weight  of  the  oxide  is  precisely  equal  to  that  of  the  oxygen 
absorbed,  whether  the  process  has  been  a  real  combustion  or  a  simple  oxida- 
tion, as  we  denominate  the  process  when  slowly  performed,  as  in  the  rust- 
ing of  iron(10). 

Emily.  You  speak,  Mrs  B.,  of  the  oxidation  or  rusting  of  iron,  as 
similar  to  combustion;  yet  in  one  there  is  a  large  portion  of  heat  disengaged, 
and  in  the  other  none  at  all. 

Mrs  B.  The  processes  are  undoubtedly  similar;  and  although  in  oxida- 
tion, from  the  extreme  slowness  of  the  operation,  you  are  not  sensible  of 
the  disengagement  of  the  heat,  yet  there  is  no  doubt  of  its  actually  being 
given  out(ll). 

Caroline.  How  high  the  water  has  risen  in  the  receiver  in  which  the 
iron  was  burnt!  much  higher  in  proportion  than  when  a  taper  was  burnt  in 
atmospheric  air. 


6.  How  long  will  such  a  wire  continue  to  burn? 

7.  What  is  the  iron  converted  into,  and  what  weight  does  it  acquire? 

8.  Is  this  an  example  of  the  decomposition  of  iron  and  oxygen? 

9.  How  far  may  it  be  said  that  decomposition  was  effected? 
10.,  What  is  remarked  on  the  acquisition  of  weight? 

11.  Why  is  not  heat  produced  in  the  oxidation  of  iron? 


116  CONVERSATIONS  ON  CHEMISTRY. 

JMrs  B.  Surely  that  cannot  surprise  you.  When  the  taper  was  burnt, 
the  whole  of  the  nitrogen  remained,  and  a  part  of  the  product  of  the  com* 
bustion  was  gaseous.  In  the  present  instance  the  whole  product  is  solid;  and 
but  for  the  difficulty  of  managing  the  combustion,  all  the  oxygen  gas  might 
be  made  to  disappear,  and  the  receiver  would,  in  lhat  case,  be  entirely  filled 
with  water  to  supply  the  vacuum(12). 

Caroline.  Pray,  Mrs  B.,  in  what  proportion  is  the  iron  increased  in 
weight  by  its  combination  with  oxygen  in  combustion? 

Mrs  B.  Its  increase  is  nearly  forty  per  cent;  that  is,  every  hundred 
grains  of  iron  which  undergo  combustion  combine  with  nearly  forty  grains 
of  oxygen.  The  increase  of  weight,  therefore,  is  not  merely  sensible,  but 
very  great(13).  This  may  serve  as  an  example  of  the  production  of  an  oxide, 
by  combustion  in  oxygen  gas.  Some  combustibles,  I  have  told  you,  are  con- 
verted into  acids  in  the  same  way;  and  potash  and  soda,  which  are  called 
alkalies,  consist  also  of  oxygen  combined  with  a  combustible.  The  products 
of  combustion  in  oxygen  are,  therefore,  divided  into  three  classes, — oxides, 
acids,  and  alkalies(l4).  I  am  anxious  that  you  should  acquire  some  general 
idea  of  these  different  classes  of  bodies,  and,  for  this  purpose,  will  give  you 
an  example  of  each  of  the  two  last  named,  reserving  a  more  particular  in- 
vestigation of  them  for  our  future  meetings. 

I  have  in  this  copper  spoon  some  pieces  of 
brimstone,  which  I  heat  over  the  candle  until 
they  begin  to  flame,  and  then  immerse  them  in 
ajar  of  oxygen. 

Caroline.  Oh,  what  a  beautiful  violet  colour- 
ed flame.  I  have  often  admired  the  flame  of 
burning  sulphur,  even  in  atmospheric  air,  but 
then  the  smell  is  most  intolerable.  In  the  pre- 
sent instance  it  burns  with  increased  brillian- 
cy and  without  any  offensive  odour. 

Emily.  The  water  is  now  rising  in  the  re- 
ceiver as  in  the  former  combustions,  proving 
that  the  oxygen  has  been  absorbed.  The  vessel  is 
entirely  filled  with  a  dense  vapour(lS).  This,  of 
course,  must  be  either  an  oxide  or  an  acid. 

Mrs  JB.     A  very  important  lesson  is  to  be 
learned  from  this  experiment.     The  nature  of     [Combustion  of  sulphur  in 
a  body  depends  not  merely  on  the  substances  oxygen  gas.] 

which  unite   together,  but  also  on  the  relative 

proportions  in  which  they  have  combined.  There  may  be  two  or  three 
different  oxides  of  the  same  metal:  thus  there  are  two  oxides  of  mercury,  one 
of  which  contains  just  twice  as  much  oxygen  as  the  other.  Several  of  the 
substances  which  are  capable  of  being  converted  into  acids,  form  two  or 
more  distinct  acids,  according  as  they  are  united  to  larger  or  smaller  pro- 
portions of  oxygen(16).  Sulphur,  when  burnt  in  atmospheric  air,  becomes 
sulphurous  acid,  which  at  common  temperatures  is  a  gas.  When  united  to  a 
larger  portion  of  oxygen,  it  becomes  sulphuric  acid,  which  we  obtain  in  the 
liquid  form  under  the  old  name  of  oil  ofvitriol(l7). 


12.  Why  does  the  water  rise  to  a  considerable  height? 

13.  What  increase  of  weight  does  the  iron  experience? 

14.  What  is  said  respecting  three  classes  of  products? 

15.  What  respecting  the  burning  of  sulphur  in  oxygen  gas? 

16.  What  is  the  fact  respecting  the  combining  of  bodies  in  different  pro- 
portions? 

17.  How  is  this  exemplified  by  the  combination  of  sulphur  and  oxygen? 


ON  OXIDES,  ACIDS,  &c.  117 

The  vapour,  or  rather  gas,  from  burning  sulphur,  the  smell  of  which  is 
so  suffocating,  is  sulphurous  acid;  while  sulphuric  acid,  although  formed  of 
the  same  materials,  is  a  liquid,  and  entirely  without  odour.  Now  this  differ- 
ence results  from  the  difference  in  their  oxygenation(lS). 

Emily.  I  suppose  that  you  have  formed  sulphuric  acid  by  burning  the 
sulphur  in  oxygen,  and  the  vapour,  which  has  now  disappeared  from  the 
glass,  was  the  sulphuric  acid  before  it  assumed  the  liquid  form. 

JWrs  B.  Not  exactly  so, — but  little  sulphuric  acid  is  formed  even  when 
sulphur  is  burnt  in  oxygen;  but  sulphurous  acid,  though  a  gas  when  in  a 
dry  state,  is,  like  many  other  gases,  capable  of  being  absorbed  by  water. 
The  vapour  which  you  saw  consisted  of  this  acid  in  the  act  of  combining 
with  the  vapour  of  water;  and  this  has  condensed,  and  formed  liquid  sul- 
phurous acid(19). 

Caroline.  I  have  always  feared  the  formidable  array  of  names  in  chem- 
istry, yet  I  confess  that  hitherto  1  have  found  none  of  the  apprehended 
difficulty;  but  I  suspect  that  we  are  now  entering  the  labyrinth,  in  which  we 
shall  find  ourselves  wofully  bewildered.  I  think,  however,  that  I  shall  re- 
member the  difference  between  sulphurous  and  sulphuric  acids. 

J\frs  B.  This  formidable  array  of  names,  as  you  are  pleased  to  denomi- 
nate the  nomenclature,  or  system  by  which  chemical  substances  are  desig- 
nated, is  one  of  the  happiest  improvements  ever  made  in  any  science,  and 
has  tended  more  than  any  other  single  circumstance  to  facilitate  the  study  of 
it(20).  When  you  are  introduced  to  a  new  substance,  you  must,  of  course, 
learn  its  name  ;  but  in  chemistry  this  extends  only  to  the  simple,  or  elemen- 
tary bodies;  the  compounds  receiving  their  names  from  combining  together 
those  of  the  substances  which  have  united.  Thus  oxygen  and  iron  form 
oxide  of  iron,  and  oxygen  and  mercury,  oxide  of  mercury(21). 

Emily.  But  I  do  not  see  how  this  applies  to  the  names  of  sulphurous 
and  sulphuric  acids;  as  we  hear,  in  these,  nothing  indicating  that  oxygen, 
enters  into  their  composition. 

Mrs.  B.  Your  objection  has  the  appearance  of  being  a  valid  one,  al- 
though it  is  not  so  in  reality.  It  was  thought  unwise  to  alter  known  and 
long  established  names  for  the  sake  of  mere  system.  A  number  of  bodies 
possessing  a  sour  taste,  and  certain  other  properties  in  common,  were  called 
acids;  and  when  it  was  believed  that  oxygen  was  the  acidifying  principle, 
the  name  of  acid  sufficiently  indicated  its  presence.  It  was  therefore  retain- 
ed, and  to  alter  it  BOW  would  be  extremely  inconvenient,  without  affording 
any  adequate  advantage(22). 

The  acids  receive  their  specific  names  from  their  bases'  thus  sulphurous 
and  sulphuric  acids  have  each  of  them  sulphur  for  its  base(23).  The 
terminations  in  ous,  and  in  ic,  indicate  that  different  proportions  of  oxygen 
have  combined  with  the  base,  whatever  that  base  may  be.  Thus,  when, 
applied  to  phosphorus,  we  have  phosphorous,  and  phosphoric  acids.  With 
the  sulphur  contained  in  sulphurous  acid,  more  oxygen  may  combine,  and 
convert  it  into  sulphuric;  or  we  may  abstract  oyxgen  from  sulphuric  acid, 
and  thus  reduce  it  to  sulphurous(24). 

Caroline.     I  am  greatly  obliged  to  you,  Mrs  B.,  for  removing  my  foolish 


18.  What  is  the  difference  between  sulphurous  and  sulphuric  acids? 

19.  What  is  produced  when  sulphur  is  burnt  in  oxygen,  and  what  form 
does  it  assume? 

20.  What  does  Mrs  B.  assert  of  the  nomenclature  of  chemistry  ? 

21.  How  are  compounds  named,  and  what  are  examples? 

22.  What  remarks  are  made  respecting  the  class  of  acids? 

23.  Whence  do  the  acids  derive  their  specific  names? 

24.  What  do  the  terminations  in  ous  and  in  ic  indicate? 


118  CONVERSATIONS  ON  CHEMISTRY. 

fears  about  names.  Whilst  speaking  of  the  acids,  I  should  like  to  learn 
some  method  of  detecting  them  besides  that  of  taste;  as  some  of  them,  I 
know,  are  very  acrid,  and  others,  I  believe,  are  poisonous. 

Mrs  B.  JJnder  the  name  of  tests,  or  reagents,  the  chemist  uses  a 
variety  of  substances  to  ascertain  the  nature  of  others.  Every  different 
body  has  a  peculiar  effect  upon  some  other  body,  and  when  such  bodies  are 
brought  together,  they  react  upon  each  other,  so  as  to  enable  us  to  deter- 
mine their  natures(25).  One  general  effect  of  acids  is  to  turn  the  blue 
vegetable  infusions  red.  I  have  in  this  wine  glass  a  blue,  or  rather  a  pur- 
ple infusion  of  red  cabbage;  a  single  drop  of  sulphuric,  or  of  any  other 
strong  acid,  will,  as  you  see,  instantaneously  change  it  to  a  red.  This  there- 
fore is  a  test  for  acids(26). 

Emily.  I  think  I  have  understood  that  the  alkalies,  which  stand  the  third 
in  your  class  of  products,  were  the  very  reverse  of  the  acids  in  their  pro- 
perties; yet  you  informed  us  a  little  while  since,  that  they  also  were  produced 
by  the  union  of  oxygen  with  a  combustible. 

Mrs  B.  There  are  a  number  of  alkaline  substances  which  we  shall 
hereafter  have  to  notice.  Two  of  these,  potash  and  soda,  you  have  frequently 
seen,  and  to  them  therefore  you  will  consider  my  present  remarks  as  con- 
fined. They  were  formerly  supposed  to  be  simple,  as  they  were  undecom- 
pounded  substances(27);  and  we  are  indebted  to  the  genius  of  the  late  Sir 
Humphry  Davy  for  a  knowledge  of  their  real  character.  The  analogy  be- 
tween them  and  some  other  substances  known  to  be  compound,  had  in- 
duced him,  in  common  with  the  greater  number  of  chemists,  to  believe  that 
they  were  actually  compounds.  Possessing  the  most  extensive  galvanic  bat- 
tery in  existence,  and  familiar  with  its  almost  resistless  power  of  decomposi- 
tion, he  submitted  a  portion  of  potash  to  its  influence,  and  obtained  oxygen 
at  the  positive  pole,  and  at  the  negative  pole  a  peculiar  metallic  substance. 
This  metallic  substance  he  named  potassium;  and  one  very  similar,  after- 
wards obtained  from  soda,  he  called  sodium(28).  I  have  in  this  phial  a  small 
portion  of  the  former. 

Caroline.  How  astonishing  that  potash  should  contain  a  metal!  It  must 
then  be  a  metallic  oxide,  and  should,  I  think,  be  so  classed.  But  why  is 
the  potassium  kept  in  a  liquid?  I  should  like  to  take  it  out  and  examine  it, 
Mrs  B.  Potash  is  really  a  metallic  oxide;  but  still  it  is  distinguished  by 
the  possession, of  those  peculiar  properties  which  belong  to  the  substances 
which  we  denominate  alkalies,  and  much  inconvenience  would  result  from 
breaking  up  this  class  of  bodies(29). 

Potassium  is  one  of  those  substances  which  have  so  strong  an  affinity  for 
oxygen  that  they  are  never  to  be  found  uncombined  with  it.  When  expos- 
ed to  the  atmosphere,  it  quickly  becomes  converted  into  potash,  or  rather 
potassa,  as  the  pure  article  is  named  by  chemists.  The  fluid  which  sur- 
rounds it  is  naphtha:  this  does  not  itself  contain  any  oxygen,  and  protects 
the  potassium  from  that  of  the  atmosphere(SO). 

Emily.  Pray  will  it  take  fire  spontaneously  when  exposed  to  the  air,  as 
you  have  told  us  is  the  case  with  some  articles? 

Mrs  B.     No;  its  combination  with  oxygen  is  not  sufficiently  rapid  for 


25.  What  is  meant  by  tests  or  reagents? 

26.  By  what  test  may  the  presence  of  an  acid  be  detected? 

27.  What  was  formerly  supposed  respecting  the  alkalies,  potash  and  soda? 

28.  Who  decomposed  the  alkalies — how — and  what  resulted? 

29.  If  then  alkalies  are  oxides,  why  not  class  them  as  such? 
SO.  Why  is  potassium  kept  under  naphtha? 


ON  OXTDES,  ACIDS,  &c.  119 

spontaneous  combustion,  excepting  water  be  present,  in  -which  case  it  burns 
with  great  rapidity(Sl). 

Caroline.  Light  a  fire  with  water!  Such  a  fact,  I  think,  may  add  another 
to  the  number  of  chemical  miracles.  What  can  water  contain  which  will 
promote  combustion? 

•Mrs  B.  Your  surprise  is  very  natural,  as  you  are  yet  uninformed  of  the 
compound  nature  of  water.  This  fluid  contains  a  large  quantity  of  oxygen, 
being  itself  a  product  of  combustion.  The  strong  attraction  of  potassium 
for  this  substance  enables  it  to  decompose  the  water  so  rapidly  as  to  produce 
combustion(32).  I  will  now  drop  a  small  piece  of  the  metal  on  the  water 
contained  in  this  bowl. 

Emily.  How  rapidly  and  how  brightly  it  has  burnt,  and  how  curiously  it 
ran  about  upon  the  surface  o£  the  water!  It  seems  to  have  been  volatilized 
in  the  process. 

Mrs  B.  Not  so:  it  has  formed  a  fixed  product  of  combustion,  which  is 
now  dissolved  in  the  water,  where  it  may  be  detected  both  by  the  taste  and 
by  other  means.  Instead  of  pure  water,  we  have  now  a  solution  of  potassa, 
with  all  its  characteristic  properties,  as  we  can  prove  by  the  same  test  which 
we  used  for  an  acid(33).  Acids  caused  the  blue  infusion  to  become  red,  but 
the  alk&li,  as  you  see,  turns  it  green(34);  and  by  carefully  dropping  a  por- 
tion of  it  into  that  which  we  reddened  by  the  acid,  the  purple  or  blue  colour 
will  be  restored,  the  alkali  counteracting  the  effects  of  the  acid  by  neutral- 
izing it(35). 

Emily  I  have  not  so  distinct  an  idea  as  I  wish  of  what  is  intended  by 
acids  and  alkalies  neutralizing  each  other,  although  this  term  is  very 
familiarly  used. 

Mrs  B.  The  acids  are  generally  distinguished  by  a  sour  taste,  and  by 
reddening  the  blue  vegetable  colours;  the  alkalies  by  a  peculiar  acrid  taste, 
and  by  changing  the  blue  infusions  to  green.  But  in  certain  proportions 
they  combine  together  and  form  a  salt,  which  is  neither  sour  nor  alkaline, 
and  which  will  not  change  the  colour  of  the  blue  infusion.  Such  a  combina- 
tion is  therefore  denominated  neutral,  although  the  salt,  as  such,  may  pos- 
sess very  active  properties(36). 

Caroline.  It  is  very  extraordinary  indeed  that  both  alkalies  and  acids 
should  depend  upon  oxygen  for  their  formation,  and  yet  possess  properties 
so  different. 

Mrs.  B.  It  is  a  striking,  but  not  an  extraordinary  fact,  as  chemistry 
abounds  with  such  examples.  Properties  the  most  contradictory  result 
from  the  combination  of  the  self  same  substances  uniting  in  different  propor- 
tions. Aquafortis,  and  the  air  we  breathe,  both  consist  of  oxygen  and  nitro- 
gen? and  plants  the  most  poisonous  and  the  most  nutritious  are  formed  by^a 
combination  of  the  same  simple  substances(37). 

You  will  now  recollect  that  when  bodies  are  burnt  in  oxygen  gas,  they 
are  converted  either  into  oxides,  acids,  or  alkalies;  and  that  it  is  not  from  an 
acquaintance  with  the  simples  which  combine  together  that  we  could  foretel 
what  would  be  the  nature  of  the  product,  but  that  we  arrive  at  this  know- 
ledge through  the  medium  of  experiment  only(38). 


31.  What  will  cause  it  to  take  fire  spontaneously? 

32.  How  does  water  cause  potassium  to  burn? 

33.  What  is  the  result  of  the  combustion? 

34.  How  may  the  presence  of  an  alkali  be  tested? 

35.  What  effect  will  this  green  fluid  produce  on  the  reddened  one? 

36.  What  is  meant  by  neutralization,  and  a  neutral  salt? 

37.  What  is  remarked  respecting  the  effect  of  chemical  combination? 

38.  What  general  fact  is  to  be  recollected  respecting  compounds? 


120  CONVERSATIONS  ON  CHEMISTRY. 

Caroline.  If  the  inquiry  is  not  out  of  place,  I  should  like  to  know  how 
the  different  oxides  of  the  same  substance  are  distinguished  from  each  other; 
us  without  some  rule  they  would  be  confounded  together. 

JWrs  JS.  Your  wish  could  not  have  been  better  timed.  The  different 
oxides  of  the  same  substance  are  rarely  of  the  same  colour,  and  they  were 
formerly  designated  from  this  circumstance;  as  the  black  oxide  and  the  red 
oxide  of  iron;  the  red  and  puce  coloured  oxides  of  lead,  &c. ;  and  this  method 
is  still  often  used(39),  although  a  better  mode  is  now  generally  pursued. 
Derivatives  from  the  Greek  are  employed  to  express  the  first,  second,  third, 
and  highest  degrees  of  oxygenation;  as  protoxide,  deutox'ide,  /nVoxide,  per- 
oxide. When  there  is  but  one  oxide  known,  no  prefix  is  needed,  it  is  merely 
called  an  oxide;  when  there  are  two,  we  say  the  protoxide  and  peroxide. 
This  mode  at  once  indicates  the  degree  of  oxidation,  and  has  several  other 
advantages  over  the  plan  of  distinguishing  the  oxides  by  their  colours 
only(40). 

Emily.  I  am  quite  in  love  with  this  system  of  names,  as  I  already  feel 
how  much  it  facilitates  the  study  of  the  science,  difficult  as  it  at  first  appear- 
ed to  be. 

Jlfrs  JB.  There  is  one  other  point  in  nomenclature  which  it  will  be  ad- 
vantageous for  you  immediately  to  learn,  and  that  is  the  mode  of  designat- 
ing the  salts.  This  is  a  very  large  and  important  class  of  bodies,  of  which 
I  can  now  give  you  only  a  very  general  idea.  Salts  are  substances  which 
consist  of  an  acid  united  to  a  base(kL).  The  alkalies,  and  metallic  oxides, 
are  bases  with  which  the  acids  unite(42),  and  the  name  given  to  any  salt 
corresponds  with  those  of  its  acid  and  base;  as  sulphate  of  potash,  which  is 
a  combination  of  sulphuric  acid  and  potash;  and  sulphate  of  iron,  which 
consists  of  sulphuric  acid  and  oxide  of  iron(43).  But  sulphurtm*  acid  may 
also  unite  to  a  base,  and  form  a  salt,  which  must  differ  from  that  formed  by 
sulphuric  acid.  When  the  name  of  the  acid  ends  in  ous,  that  of  the  salt  ter- 
minates in  itej  when  in  ic,  it  becomes  ate.  Thus  sulphurous  acid  with 
potash,  forms  sulplwYe  of  potash;  and  sulphuric  acid  produces  sulphate  of 
potash.  The  same  remark  will  apply  to  phosphoric  and  phosphorous 
acids,  and  to  several  others(44). 

The  same  acid,  in  some  instances,  combines  with  the  same  base  in  dif- 
ferent proportions,  and  this  difference  also  requires  to  be  designated(45). 
Salts  were  formerly  divided  into  neutral  salts,  swpersalts,  and  sw6salts. 
They  were  called  neutral,  when  the  acid  and  alkali  were  in  those  propor- 
tions which  neutralized  each  other,  supersalts  if  the  acid  prevailed,  and 
subsalts  if  the  alkali  was  in  excess.  Sulphate  of  potash,  supersulphata 
of  potash,  and  subsulphate  of  potash,  might  serve  as  examples,  although,  in 
fact,  the  latter  is  not  known(46). 

We  now  apply  the  Latin  numerals  to  the  salts,  as  the  Greek  are  used  to 
the  oxides;  employing  them  to  distinguish  the  proportion  which  the  acid 
and  the  base  bear  to  each  other,  as  bis  for  doubled,  ter  for  tripled,  and 
quater  for  quadrupled.  Thus  we  say  sulphate  of  potassa,  and  ^'sulphate 


39.  How  have  the  different  oxides  of  the  same  substance  been  distin- 
guished ? 

40.  How  are  they  now  most  commonly  distinguished? 

41.  What  is  understood  by  a  salt? 

42.  What  are  bases  with  which  the  acids  combine  and  form  salts? 

43.  Give  examples  of  the  nomenclature  of  salts. 

44.  How  is  the  state  of  the  acid  in  the  salt  distinguished? 

45.  What  is  remarked  respecting  the  same  acid  and  base? 

46.  How  were  their  different  states  distinguished  from  each  other! 


ON  HYDROGEN  AND  OXYGEN.  121 

ofpotassa;  the  first  consisting  of  a  single  atom,  or  proportional,  of  acid  and 
of  base,  and  the  second,  of  two  atoms  of  acid  to  one  of  base(47). 

From  the  combination  of  oxalic  acid  and  potassa  in  different  proportions, 
we  have  oxalate  ofpotassa,  dmoxalate  of  potassa,  and  guadroxalate  of  potassa; 
because  one  atom,  or  proportional,  of  the  alkali  is  united  with  one  of  the 
acid  in  the  first,  with  two  in  the  second,  and  with  four  in  the  third  salt(48). 

I  have  now  given  you  by  far  the  most  difficult  lesson  on  the  subject  of 
names  which  you  -will  have  to  learn,  but  am  certain  from  your  attention 
that  you  will  have  mastered  it,  or  nearly  so,  by  the  time  of  our  next  meet- 
ing, when  we  shall  take  up  the  subject  of  hydrogen,  and  its  combinations 
•with  oxygen. 

Caroline.  I  certainly  am  not  anxious  to  enter  further  into  the  details  of 
nomenclature,  before  ruminating  upon  what  you  have  already  taught  us;  but 
before  we  part,  allow  me  to  ask  why  nitrogen  is  also  called  azote. 

•Mrs  B.  The  term  azote  originated  with  Lavoisier  and  his  associates.  It 
is  derived  from  the  Greek,  and  signifies  to  destroy  life^  but  as  azote  was 
found  to  be  the  base  of  nitric  acid,  which  is  obtained  from  nitre,  chemists 
have  generally  concurred  in  preferring  the  name  nitrogen  to  that  of  azote(49). 


CONVERSATION  XII. 

ON  HYDROGEN,  AND  ITS  COMBINATIONS  WITH  OXYGEN. 

Water  a  Compound  Substance.  Conjecture  of  Sir  Isaac  Newton.  In- 
Jiammable  Air.  Natural  Sources  of  Hydrogen.  Formation  of  Water.  Hy- 
drogen always  obtained  from  this  Fluid.  Processes  by  -which  Hydrogen  ii 
obtained.  Used  for  filing  Air  Balloons.  Proofs  of  its  Levity.  Explodes 
•with  Oxygen.  Proportionate  quantities  of  each.  Discovery  of  the  Compo- 
sition of  Water.  Large  quantity  formed  by  the  French  Chemists.  Musical 
Tones  in  Glass  Tubes.  Soap  Bubbles  filed  -with  Hydrogen  alone  and  in 
mixture.  Some  properties  of  Water.  Deutoxide  of  Hydrogen. 

Caroline.  I  feel  an  unusual  degree  of  interest  in  the  subject  which  is  to 
claim  our  attention  this  morning;  for  although  I  have  not  the  least  doubt  of 
the  fact,  I  find  some  difficulty  in  realizing  the  idea  that  what  we  have  so 
often  heard  called  simple  water,  is  a  compound. 

JMrs  B.  The  compound  nature  of  water  lies  at  the  very  foundation  of 
the  modern  system  of  chemistry,  and  the  evidences  of  its  truth  are  so  nu- 
merous and  so  perfect,  as  altogether  to  defy  scepticism(l).  You  cannot 
have  forgotten  the  acute  and  extraordinary  conjecture  of  sir  Isaac  Newton, 
•which  was  mentioned  in  our  Conversations  on  Natural  Philosophy,  that  water 
resisted  in  part  of  a  principle  which  was  uninflammable,  and  in  part  of  one 
•which  he  denominated  oily,  unctuous,  or  inflammable.  The  conjecture  of 
this  great  man  has  been  fully  verified,  and  presents  itself  to  us  as  one  of  the 
strongest  examples  of  the  value  of  reasoning  from  analogy,  when  conducted 
•with  that  caution  which  belongs  to  true  philosophy(2). 

Hydrogen  gas,  the  base  of  which  is  one  of  the  constituents  of  water,  was 


47.  What  method  is  now  adopted?  and  give  examples. 

48.  Give  the  example  of  the  combinations  of  oxalic  acid  with  potassa. 

49.  What  is  observed  respecting  the  names  azote  and  nitrogen? 

1.  What  remarks  are  made  concerning  the  compound  nature  of  water? 

2.  What  respecting  Sir  Isaac  Newton's  conjecture  on  this  subject? 

L 


122  CONVERSATIONS  ON  CHEMISTRY. 

formerly  called  inflammable  air,  as  it  takes  fire  readily  and  burns  with 
flame(3).  This  gas,  combined  usually  with  some  other  inflammable,  has 
been  long  known  as  a  natural  product,  being  disengaged  in  coal  mines, 
from  certain  springs,  and  also  -from  fissures  in  the  ground,  where  it  takes 
fire  when  a  light  is  applied  to  it(4).  When  it  was  found  to  be  one  of  the 
constituents  of  water,  it  received  the  name  of  hydrogen,  which  is  derived 
from  two  Greek  words  signifying  to  produce  water(5). 

Emily.     And  how  does  hydrogen  produce  water? 

Mrs  B.  By  its  combustion,  in  which  it  unites  with  oxygen.  Water  is 
composed  of  eight  parts  by  weight  of  oxygen,  combined  with  one  part  of 
hydrogen(6).  If  the  estimation  is  made  by  the  volume,  or  bulk,  of  the  gases, 
we  must  take  twice  as  much  of  the  hydrogen  as  of  the  oxygen,  the  specific 
gravity  of  oxygen  exceeding  that  of  hydrogen  sixteen  times.  The  latter,  in 
the  gaseous  state,  is  the  lightest  natural  body  known(7). 

Caroline.  And  is  it  really  possible  that  water  should  be  a  combination  of 
two  gases,  and  that  one  of  these  should  be  inflammable  air!  Hydrogen 
must  be  a  most  extraordinary  gas  to  produce  both  fire  and  water. 

Mrs  B.  You  should  rather  say  that  water  is  a  combination  of  the  bases 
of  two  gases;  for  when  they  combine  they  lose  their  gaseous  form(8). 

Emily.  But  I  thought  you  said  that  combustion  could  take  place  in  no 
gas  but  oxygen. 

Mrs  B.  Do  you  recollect  in  what  the  ordinary  process  of  combustion 
consists? 

Emily.  In  the  combination  of  a  body  with  oxygen,  accompanied  by  thfc 
disengagement  of  light  and  heat. 

Mrs  B.  When,  therefore,  I  say  that  hydrogen  is  combustible,  I  mean  that 
it  readily  combines  with  oxygen.  But,  like  all  other  combustible  substances, 
it  cannot  burn  unless  supplied  with  oxygen,  and  also  heated  to  a  proper  tem- 
perature^). 

CaroliKS.  The  simply  mixing  two  parts  by  bulk  of  hydrogen,  with  one 
part  of  oxygen  gas,  will  not,  therefore,  produce  water. 

MrsB.  No;  water  being  a  much  more  dense  fluid  than  the  gases,  it  is  ne- 
cessary 3  in  order  to  reduce  these  gases  to  a  liquid,  that  they  should  part  with 
the  caloric  which  maintains  them  in  an  elastic  form(10).  But  we  had  better 
proceed  at  once  to  the  decomposition  of  water,  and  the  obtaining  of  hydro- 
gen gas  from  it,  in  order  to  exhibit  its  properties.  Hydrogen  is  contained 
in  many  other  substances  besides  water;  but  whenever  we  wish  to  obtain  it 
in  a  pure  state,  this  is  always  effected  by  the  decomposition  of  that  fluid(ll). 

Qaroline.  I  should  like  extremely  to  see  water  decomposed.  Is  there 
more  than  one  method  of  doing  this? 

Mrs  B.  Yes,  several.  There  are  a  number  of  combustible  bodies,  which 
at  the  temperature  of  ignition  have  a  stronger  affinity  for  the  oxygen  of  the 
water  than  hydrogen  has,  and,  consequently,  if  water  in  the  state  of  vapour 
be  brought  into  contact  with  them,  they  will  deprive  it  of  its  oxygen,  and 
the  hydrogen  will  be  liberated  in  the  gaseous  forrn(12).  Either  charcoal 


3.  Why  was  hydrogen  gas  called  inflammable  air? 

4.  Is  it  produced  naturally,  and  in  what  situations? 

5.  From  what  is  its  name,  hydrogen,  derived? 

6.  How  is  water  formed,  and  what  are  its  constituents? 
7:  In  what  proportion,  by  volume,  do  the  gases  combine? 

8.  Is  it  proper  to  say  that  the  gases  form  water? 

9.  What  is  meant  when  we  say  that  hydrogen  is  combustible? 

10.  With  what  must  the  gases  part,  when  changed  to  liquids? 

11.  From  what  is  hydrogen  gas  always  obtained? 

12.  Upon  what  principle  may  water  be  decomposed? 


ON  THE  DECOMPOSITION  OF  WATER.  123 

ot  iron,  -when  ignited,  will  decompose  water,  and  when  the  latter  is  em- 
ployed the  hydrogen  may  be  obtained  in  great  purity(13). 

Emily.  As  the  hydrogen  is  combustible,  I  am  puzzled  to  tell  how  you 
can  keep  it  from  burning,  when  in  contact  with  red  hot  iron. 

Mrs  B.  There  are  methods  of  decomposing  water  which  are  much  more 
easy  than  that  by  heated  iron,  which  is  indeed  a  very  troublesome  one;  but 
as  it  is  one  of  the  most  direct  and  satisfactory,  I  will  exhibit  to  you  the  ap- 
paratus by  which  it  is  effected,  and  explain  its  operation,  but  without  at- 
tempting any  actual  experiment.  This  will  save  much  time,  and  answer 
every  useful  purpose. 

Furnace  and  gun  barrel  for  decomposing  -water 


[A,  the  furnace.  B,  the  gun  barrel,  filled  with  iron  wire  in  the  heated 
part.  C,  retort,  with  water  kept  boiling.  D,  the  tube  which  conducts 
the  hydrogen  into  the  receiver  E,  placed  over  water.  ] 

This  is  a  small  furnace  in  which  most  of  the  metals  may  be  melted,  and 
other  processes  performed  which  require  considerable  heat.  Through  two 
openings  in  its  sides  any  tube  which  it  is  desired  to  heat  may  be  passed.  Some 
iron  wire  or  other  shreds  of  iron  are  rammed  into  the  middle  of  a  clean  gun 
barrel,  so  as  to  occupy  a  length  of  six  or  eight  inches.  A  small  retort, 
half  filled  with  water  is  luted  into  the  opening  at  one  end.  Strips  of  paper 
pasted  round  the  joining  answer  this  purpose  perfectly  well.  From  the 
other  end  a  bent  tube  passes  into  a  receiver  for  collecting  the  gas.  When 
the  fire  is  lighted  and  the  gun  barrel  so  placed  that  the  part  containing  the 
shreds  of  iron  is  exposed  to  the  fire,  it  soon  becomes  red  hot,  and  the  water 
in  the  retort,  being  in  the  mean  time  made  to  boil,  the  steam  is  compelled 
to  pass  over  the  ignited  iron,  which  will  decompose  it(14). 

Caroline.  Now  I  think  that  I  can  tell  how  this  decomposition  is  effected; 
the  strong  attraction  of  the  ignited  iron  for  oxygen,  enables  it  to  take  it 
from  the  hydrogen,  which  escapes  in  the  gaseous  form.  But,  like  Emily,  I 
am  at  a  loss  to  know  why  so  inflammable  a  substance,  so  highly  heated,  does 
not  burn(15). 

•Mrs  B.  Yet  if  I  ask  you  what  is  necessary  to  its  combustion,  you  will 
answer,  an  elevation  of  temperature,  and  the  presence  of  oxygen;  now  tell 
me,  how  it  is  to  obtain  the  latter? 


13.  What  two  articles  are  named  which  will  decompose  water? 

14.  Describe  the  apparatus  used  for  its  decomposition. 

15.  How  does  the  iron  operate  in  promoting  it? 


124  CONVERSATIONS  ON  CHEMISTRY. 

Caroline.  Why  did  we  not  think  of  that  Emily  I  The  oxygen  of  the  water 
is  taken  away  from  it  by  the  iron,  and  though  highly  heated,  it  is  not  expos- 
ed to  the  atmosphere,  or  to  any  other  source  of  oxygen,  and  therefore  cannot 
burn(16). 

Emily.  Water  then  must  be  an  oxide  of  hydrogen,  yet  you  do  not  call 
it  so;  and  the  iron,  in  the  process  you  have  described,  must  also  be  convert- 
ed into  an  oxide  of  iron(17). 

Mrs  B.  Very  well  said.  Strictly  speaking,  water  is  an  oxide,  but  I  am 
sure  you  will  not  complain  of  its  familiar  name  being  retained.  The  iron  is, 
as  you  correctly  observed,  converted  into  an  oxide,  and  is  exactly  similar  to 
that  produced  by  the  burning  of  iron  wire  in  oxygen  gas.  It  will,  of  course, 
be  found  to  have  acquired  weight  from  the  same  cause.  Were  we  to  weigh 
the  hydrogen  obtained,  we  should  finoMhat  for  every  grain  of  it,  the  iron  had 
acquired  an  addition  of  eight  grains(18). 

Caroline.  This  is  altogether  as  direct  and  satisfactory  a  proof  of  the 
composition  of  water  as  could  be  desired.  But  I  see  that  you  have  the  vol- 
taic battery  upon  the  table?  I  have  been  anxious  to  see  its  power  exhibited 
in  decomposing  bodies. 

.Apparatus  for  the  decomposition  of  -water  by  the  voltaic  battery. 


Mrs  JB.  And  you  will  now  witness  it  in  its  action  upon  water,  as  that 
fluid  can  be  very  readily  decomposed  by  it.  For  this  purpose  I  fill  this 
erooked  glass  tube  with  water,  and  cork  it  up  at  both  ends.  Through  one  of 
the  corks  I  introduce  a  wire  which  is  connected  with  the  positive  pole  of  the 
battery,  whilst  the  wire  that  is  connected  with  the  negative  pole  is  made  to 
pass  through  the  other  cork.  The  two  wires  approach  each  other  suffi- 
ciently near  for  the  electrical  current  to  take  place. 

Caroline.  It  does  not  appear  to  me  that  you  cause  the  wires  to  approach 
so  near  as  you  formerly  did  when  you  used  the  battery. 

Mrs  B.  Water  being*a  better  conductor  of  electricity  than  air,  the  two 
wires  will  act  on  each  other  at  a  greater  distance  in  the  former  fluid  than 
in  the  latter. 

Emily.  Now  the  electrical  effect  appears:  I  see  small  bubbles  of  air 
emitted  from  each  wire. 

Mrs  B.  Each  wire  acts  in  decomposing  the  water;  the  positive  by  at- 
tracting its  oxygen,  which  is  negative;  the  negative  by  attracting  its  hydro- 
gen, whkh  is  positive(19). 

Caroline.  That  is  wonderfully  curious!  but  what  are  the  small  bubbles 
of  air? 

Mrs  B.  Those  that  proceed  from  tne  positive  wire,  are  the  result  of  the 
attraction  of  the  oxygen  of  the  water,  which  is  electro-negative.  This  com- 
bining with  caloric  is  by  that  wire  set  at  liberty,  and  appears  in  the  form  of 
small  bubbles  of  gas  or  air.  In  like  manner  the  hydrogen,  which  is  electro- 


16.  Why  does  not  the  hydrogen  burn  when  so  highly  heated? 

17.  What  does  Emily  remark  respecting  the  water  and  the  iron? 

18.  To  what  will  the  increased  weight  of  the  iron  be  equal? 

19.  Describe  the  decomposition  of  water  by  the  voltaic  battery. 


ON  THE  DECOMPOSITION  OF  WATER.  125 

positive,  is  attracted  towards  the  negative  pole,  and  produces  the  more  nu- 
merous bubbles  which  you  see  are  disengaged  in  contact  with  that  wire(20). 

You  must  not,  however,  neglect  to  observe,  that  the  wires  used  in  this 
experiment  are  made  of  platina,  a  metal  which  is  not  capable  of  becoming 
oxidized;  for  otherwise  the  wire  would  combine  with  the  oxygen,  and  the 
hydrogen  alone  would  be  disengaged(21). 

Caroline.  But  could  not  water  be  decomposed  without  the  electric  circle 
being  completed?  If,  for  instance,  you  immersed  only  the  positive  wire  in 
the  water,  would  it  not  combine  with  the  oxygen,  and  the  hydrogen  gas  be 
given  out? 

Mrs  B.  By  no  means;  the  battery  cannot  act  unless  the  electric  circle  be 
completed,  so  that  the  fluid  can  find  a  passage  from  one  pole  to  the  other(22). 

Caroline.    I  understand  it  'now.     But  look,  Mrs 

B.,  the  decomposition  of  the  water,  which  has  been  Decomposing  -water 
going  on  for  some  time,  does  not  sensibly  diminish  by  Voltaic  Electricity, 
its  quantity;  what  is  the  reason  of  that?  and  collecting  the  gases 

Mrs  B.  Because  the  quantity  decomposed  is  so  separately. 
extremely  small.  If  you  compare  the  density  of 
water  with  that  of  the  gases  into  which  it  is  re- 
solved, you  must  be  aware  that  a  single  drop  of  wa- 
ter is  sufficient  to  produce  thousands  of  such  small 
bubbles  as  those  you  now  perceive. 

Caroline.  But  in  this  experiment,  we  obtain  the 
oxygen  and  hydrogen  gases  mixed  together.  Is  there 
any  means  of  procuring  the  two  gases  separately? 

Mrs  B.  They  can  be  collected  separately  with 
great  ease  by  modifying  the  experiment  with  that 
riew.  Instead  of  one  tube,  two  may  be  employed, 
as  in  this  apparatus.  Two  platina  wires  pass  through 
openings  on  opposite  sides  of  this  glass  vessel,  which, 
you  see,  contains  water.  Over  the  inner  ends  of 

these  wires  are  two  tubes  filled  with  water  their  eCiththe  negate;  6~ 
lower  ends  being  open,  and  their  upper  ends  closed.  that  CQnnectJd  with 
On  connecting  the  two  wires  with  the  opposite  poles  ,  nositive  ^^  of 
of  a  battery,  the  „„»  of  the  water  will  be  dUen-  rf 


gaged  at  one  wire,    and  the  hydrogen  at  the  other.  throusrh  nerfora- 

This  wire  [6]  is  positive,  and  will  attract  the  oxy-  J'  ougn  pe 

,.,.,,  ,.         i         ,     r  TT    i         •          i   tions  in   a  goblet  con- 

gen,  which  will  ascend  into  the  tube  [d]  above  it;  and      .   . 


as  the  other  wire  [a]  is  negative,  the  hydrogen  will  £»  5J33?  receives 
ascend  into  this  tube  [c],  and  its  volume  will  be  ex-          fc  rf    that 

actly  double  that  of  the  oxygen;   these  being  the  ,.       ^e  OXyeen 
precise  proportions  which  form  water(23). 

Emily.  Then  if  we  were  to  burn  the  hydrogen,  by  means  of  the  oxygen, 
they  would  again  reproduce  the  exact  quantity  of  water  that  has  been  de- 
composed^). We  however  shall  be  a  long  time  in  collecting  enough  for 
that  purpose.  I  am  sorry  that  the  decomposition  by  metals  is  so  inconve- 
nient, as  it  would  be  very  satisfactory  to  experiment  with  the  hydrogen  upon 
a  larger  scale. 

Mrs  B.  Hydrogen  is  as  readily  obtained  in  large  quantities  as  any  of 
the  gases,  "but  by  a  process,  the  explanation  of  which  is  more  complex  than 


20.  In  what  way  was  tWe  principle  of  its  operation  explained? 

21.  Why  are  platina  wires  used  in  the  experiment? 

22.  For  what  reason  must  the  electric  circle  be  completed? 

23.  Describe  the  apparatus  for  obtaining  the  gases  separately? 

24.  Were  these  gases  reunited,  what  would  be  the  consequence? 

L  2 


126  CONVERSATIONS  ON  CHEMISTRY. 

those  which  you  have  already  seen;  the  intervention  of  an  acid  being  neces- 
sary to  quicken  the  oxidation  of  the  metal  employed. 

Instead  of  a  retort,  I  take  a  common  sweet  oil  flask,  having  a  bent  tube 
passing  through  a  cork  which  fits  into  the  neck  of  it.  By  this  simple  and 
cheap  contrivance  nearly  all  the  processes  may  be  performed  for  which  re- 
torts or  alembics  are  usually  employed;  whilst  a  common  tub  or  bucket 
will  make  a  good  pneumatic  cistern,  and  tumblers  and  phials  answer  as  re- 
ceivers for  the  gases(25). 

Into  the  flask  I  put  about  an  ounce  of  tacks,  or  other  small  pieces  of  iron, 
and  about  a  gill  of  water;  upon  these  I  pour,  slowly,  about  one  fifth  part  as 
much  sulphuric  acid  (oil  of  vitriol)  as  there  is  water.  The  mixture  will 
immediately  become  hot,  and  bubbles  of  air  will  be  rapidly  disengaged. 
I  now,  therefore,  fix  the  tube  into  the  neck  of  the  flask,  and  collect  the  gas 
in  the  receiver(26). 

Jl  tub  used  as  a  pneumatic  cistern,  and  hydrogen  procured  by  means  of  a 
Jlorence  flask  and  phials. 


Caroline.  Bless  me,  how  rapidly  it  comes  over;  the  receiver  is  already 
filled  and  the  gas  escaping.  The  acid  does  indeed  quicken  the  action,  but 
then  it  leaves  it  doubtful  whether  the  hydrogen  may  not  proceed  from  some 
other  source  besides  the  water. 

JMrs  JB.  Certainly  such  a  doubt  might  be  very  fairly  entertained  if  the 
subject  had  not  been  investigated;  but  it  can  easily  be  proved  that  the  whole 
of  the  acid  and  of  the  iron  remains  in  the  flask,  united  together,  and  with 
the  oxygen  of  that  portion  of  the  water  which  has  been  decomposed(27). 

Emily.  As  neither  of  the  ingredients  used  is  quite  new  to  us,  I  think, 
Mrs  B.,  that  with  your  aid  we  might  understand  the  process  which  has 
taken  place,  although  it  may  be  rather  complex. 

Mrs  JB.  If  we  had  merely  put  the  iron  into  the  water,  the  attraction  be- 
tween the  metal  and  the  oxygen  would  not  have  been  sufficiently  powerful  to 
have  decomposed  the  water(28);  but  the  acids,  you  may  recollect,  will  com- 
bine with  the  oxides  of  the  metals,  and  form  salts,  there  being  a  strong  at- 


25.  By  what  simple  apparatus  may  the  gases  be  obtained? 

26.  What  articles  are  put  into  the  retort  or  flask? 

27.  What  proof  exists  that  water  alone  furnishes  the  hydrogen? 

28.  Why  would  not  the  iron  alone  decompose  the  water? 


ON  THE  PROPERTIES  OF  HYDROGEN.  127 

traction  between  them.  It  is  probable  that  when  we  put  apiece  of  iron  into 
water,  a  thin  film  of  oxide  is  formed  upon  its  surface,  which  oxide  being 
insoluble  in  water,  defends  it  from,  being  further  acted  upon;  but  if  we  sup- 
ply sulphuric  acid,  this  dissolves  the  oxide,  and  a  new  film  of  oxide  is  formed, 
and  instantaneously  dissolved.  The  combined  attraction  of  the  iron  for 
oxygen,  and  of  sulphuric  acid  for  the  oxide  of  iron,  operating  simultaneous- 
ly, thus  effects  the  decomposition(29). 

Emily.  I  can  readily  conceive  that  where  two  attractions  are  operating, 
an  effect  may  be  produced  for  which  one  would  be  insufficient;  but  still  I  do 
not  exactly  see  how  the  hydrogen  gas  is  produced,  or  what  proof  exists  that 
it  is  derived  from  the  water  alone. 

Mrs  B.  If,  after  the  action  has  entirely  ceased,  we  were  to  evaporate  the 
whole  of  the  water  from  the  other  contents  of  the  flask,  we  should  obtain 
crystals  of  sulphate  of  iron  (common  copperas)  in  such  quantity  as  to  contain 
the  whole  of  the  acid  employed,  and  the  whole  of  the  iron  which  has  been 
dissolved.  When  the  materials  were  placed  together,  the  oxygen  of  a  por- 
tion of  the  water  united  to  the  iron;  whilst  its  hydrogen,  having  nothing  to 
combine  with,  assumed  the  gaseous  form,  and  escaped.  The  sulphuric  acid 
combined  with  this  oxide  and  formed  the  salt  called  sulphate  of  iron;  and  so 
long  as  there  was  any  undecomposed  water,  and  any  uncombined  sulphuric* 
acid  and  iron,  we  might  continue  to  collect  hydrogen  gas(30). 

Caroline.'  I  think  that  I  understand  your  explanation  perfectly.  But 
may  not  other  metals  and  acids  be  employed  besides  those  which  you  have 
used? 

Mrs  B.  Yes,  but  the  cheapness  of  sulphuric  acid,  and  the  facility  with 
which  iron  may  be  obtained,  cause  them  to  be  generally  preferred.  An  acid 
called  muriatic  acid  is  sometimes  employed,  and  the  metal  called  zinc  is 
often  preferred  to  iron;  because  the  gas  thus  obtained  has  a  less  unpleasant 
odour  than  that  from  iron(31). 

Emily.  Then  there  must  be  some  difference  in*  the  gases,  or  their  odour 
would  be  the  same. 

Mrs  B.  Remember  what  I  told  you  respecting  the  procuring  of  articles 
absolutely  pure.  Neither  iron,  nor  zinc,  as  we  usually  find  them,  are  so, 
and  the  odour  of  the  gas  results  from  its  dissolving  a  small  portion  of  these 
impurities. 

We  have  now  a  sufficient  quantity  of  the  gas  collected  for    Plate  -with  re- 
our  experiments.    By  means  of  a  plate  I  can  readily  remove        ceiver  filled 
one  of  the  receivers  from  the  shelf  of  the  cistern,   either       -with  air. 
to  make  room  for  others,  or  to  use  it  whenever  it  may  be 
wanted.    I  merely  introduce  the  plate  under  the  water,   and 
slide  the  receiver  on  it;  the  water  in  the  plate  as  effectually 
confining  the  gas,  as  does  that  in  the  cistern(32). 

Emily.  I  am  quite  surprised  to  see  what  a  large  quanti- 
ty of  hydrogen  can  be  produced  by  a  small  quantity  of  water, 
especially  as  oxygen  is  the  principal  constituent  of  that  fluid. 

Mrs  B.  In  weight  it  is,  but  not  in  volume.  ,  You  forget 
that  the  volume  of  hydrogen  gas,  when  water  is  decomposed, 
is  double  that  of  the  oxygen.  Hydrogen  gas  I  have  told  you  is 
the  lightest  body  in  nature.  It  is  sixteen  times  lighter  than 
oxygen,  which  itself  is  eight  hundred  times  lighter  than  wa- 
ter. By  a  very  easy  calculation,  therefore,  you  will  find  that  the  hydrogen 


29.  How  does  the  acid  act  in  promoting  the  decomposition? 

30.  In  what  way  is  the  whole  action  explained? 

31.  What  other  materials  will  answer  the  same  purpose? 

32.  How  may  the  gas  collected  be  removed  from  the  cistern? 


128  CONVERSATIONS  ON  CHEMISTRY. 

produced  will  exceed  the  bulk  of  water  decomposed,  about  seventy -five  thou- 
sand times(  33).  It  is  on  account  of  its  levity  that  it  is  employed  for  filling  air 
balloons,  which  float  in  the  atmosphere  in  consequence  of  their  displacing 
a  weight  of  common  air  greater  than  that  of  the  hydrogen,  the  balloon,  and 
its  appendages.  It  is  for  this  same  reason  that  a  substance  lighter  than  water 
floats  on  that  fluid(34). 

Caroline.     Can  we  not  fill  abladderwith  this  gas,  and  cause  it  to  ascend? 

Mrs  B.  No;  a  bladder  cannot  be  made  sufficiently  thin  and  light  for 
this  purpose;  but  you  will  presently  see  how  rapidly  soap  bubbles  filled 
•with  hydrogen  will  rise  in  the  atmosphere.  I  will  first  however  show  you 
its  inflammability,  which  is  one  of  its  most  important  properties;  as  it  is 
concerned  in  most  of  the  combustions  which  are  accompanied  by  flame. 

Into  this  bottle  [Fig.  1.]  I  put  the  materials  for  making  hydrogen,  and  insert 
a  tube,  fitted  by  means  of  a  cork,  into  the  neck  of  it.  Through  this  tube  the 
gas  will  issue  in  a  continued  stream,  and  when  lighted  will,  as  you  see,  con- 
tinue to  burn.  This  is  sometimes  called  the  philosophical  candle(35). 

Philosophical  Candle.  Two  glass  vessels  for  showing  the  le- 

vity of  hydrogen  gas. 


Fig.  2. 
Fig.  1. 


Emily.  How  prettily  it  burns  with  a  beautiful  pale  blue  flame.  I  sup- 
pose that  the  product  of  its  combustion  is  nothing  but  water. 

Jlfrs  £.  You  are  right;  and  were  we  to  collect  it  we  should  find  that 
every  grain  of  hydrogen  had  combined  with  eight  grains  of  the  oxygen  of 
the  atmosphere,  and  produced  nine  grains  of  water(36). 

Before  showing  you  another  experiment  on  its  inflammability,  I  will  ex- 
hibit to  you  one  which  will  manifest  its  levity.  I  fill  these  two  glasses  with 
hydrogen,  and  place  them  with  the  open  mouth  of  one  up,  and  of  the  other 
down.  [Fig.  2.]  We  may  allow  them  to  remain  for  several  minutes  in  this 
situation,  when  on  applying  a  taper  to  that  with  the  mouth  up,  it  will  be 


S3.  Why  is  the  volume  of  hydrogen  produced  so  great? 

34.  Why  are  air  balloons  filled  with  hydrogen  gas? 

35.  What  is  it  that  is  called  the  philosophical  candle? 

36.  What  is  said  respecting  the  product  of  its  combustion? 


ON  THE  PROPERTIES  OF  HYDROGEN. 


129 


found  to  contain  atmospheric  air  only;  whilst  the  gas  -will  still  remain  in  the 
Other,  and  will  take  fire,  and  burn(37). 

Caroline.  In  this  case  the  hydrogen  being  lighter  than  the  common  air, 
ascended  from  the  first  glass,  and  the  atmosphere  occupies  its  place;  whilst 
the  very  levity  of  the  hydrogen  tended  to  keep  it  in  the  inverted  glass,  as  it 
could  not  ascend  through  it(38). 

Mrs  B.  Upon  this  principle  a  receiver  may  be  filled  with  hydrogen, 
without  the  use  of  a  pneumatic  cistern;  by  taking  a  bottle  and  tube  similar 
to  that  which  we  used  for  the  philosophical  candle,  and  allowing  the  gas 
to  escape  through  the  tube,  and  pass  into  a  receiver  held  over  it.  [Fig.  1.] 
It  will  by  its  levity  rise  to  the  top  of  the  receiver,  and  as  it  accumulates 
will  force  the  atmospheric  air  out,  and  occupy  its  place(39). 

This  same  principle  may  be  applied  to  gases  which  are  heavier  than  at- 
mospheric air;  but  in  this  case  the  tube  must  be  bent  so  as  to  pass  down  to 
the  bottom  of  a  bottle,  standing  with  its  mouth  upwards:  this  you  will  wit- 
ness at  a  proper  time.  Gases  which  are  absorbed  by  water  may  also  be 
sometimes  thus  collected,  all  of  them  being  either  heavier  or  lighter  than 
atmospheric  air. 

'Emily.  We  feel  much  obliged,  Mrs  B.,  by  this  kind  of  information,  as  it 
will  enable  us  sometimes  to  try  an  experiment  which  we  otherwise  could 
not  attempt  from  want  of  the  usual  means. 


Filling'  receiver  -with  hydrogen  gas 
•without  using  a  pneumatic  cistern. 


Candle  extinguished  and  relighted 
by  hydrogen. 


Fig.  1. 


Fig  2. 


Mrs  B.  I  pass  this  inverted  phial  of  hydrogen  over  this  lighted  candle. 
[Fig.  2.]  The  gas  takes  fire  as  soon  as  it  touches  the  flame,  and  continues  to 
burn  at  the  mouth  of  the  vessel;  but  the  candle  is  extinguished  the  moment  it 
is  completely  immersed  in  the  hydrogen,  and  is  relighted  in  passing  through 
the  flame  when  I  withdraw  it;  and  this,  as  you  see,  can  be  repeated  a  num- 
ber of  times(40). 

Caroline.  I  am  delighted  with  this  experiment,  it  exemplifies  so  clearly 
the  difference  between  a  combustible  and  a  supporter  of  combustion. 
What  you  have  told  us  about  oxygen  explains  the  whole.  Without  this 


37.  How  may  its  levity  be  shown  by  two  glasses? 

38.  In  what  way  is  this"  phenomenon  explained? 

39.  How  may  hydrogen  gas  be  collected  without  a  pneumatic  cistern? 

40.  What  experiment  is  performed  with  hydrogen  and  a  candle? 


130  CONVERSATIONS  ON  CHEMISTRY. 

same  oxygen,   neither  the  hydrogen  nor  the  candle  can  hum.      There  is  no 
oxygen  in  the  phial,  and  therefore  the  candle  is  extinguished;  but  at  its  mouth 
,the  oxygen  of  the  atmosphere  keeps  up  the  combustion,  and  your  philoso- 
phical candle  relights  your  common  one(4l). 

Mrs  B.  Your  happy  application  of  what  you  have  already  learned,  is  to 
me  a  most  gratifying  recompense  for  the  little  time  which  I  have  devoted  to 
your  instruction.  I  have  nothing  to  add  to  the  explanation  which  you  have 
given,  but  will  proceed  to  show  you  some  other  examples  of  the  combustion 
of  hydrogen.  Did  you  not  observe  that  when  we  set  fire  to  the  hydrogen, 
at  the  mouth  of  the  jar,  that  it  kindled  with  a  slight  explosion? 

Emily.  Yes,  and  I  was  just  about  to  ask  you  the  cause  of  this,  as  it  after- 
wards burnt  so  quietly  and  silently. 

Mrs  B.  Just  at  the  mouth  of  the  jar,  the  oxygen  of  the  atmosphere,  and  a 
portion  of  the  hydrogen  had  intermingled.  The  whole  of  this  portion  there- 
tore  took  fire  instantaneously,  every  particle  of  hydrogen  being  in  contact 
with  a  particle  of  oxygen(42).  Can  you  not  perceive  what  would  be  the 
consequence  were  we  to  ignite  the  two  gases  in  a  state  of  complete  mixture. 
Emily.  I  think  I  do:  as  a  slight  explosion  was  produced  by  a  small  por- 
tion, I  should  apprehend  that  a  larger  quantity  would  explode  with  corres- 
ponding power(43). 

Mrs  B.     And  such  is  the  fact.      Observe  that  I  fill  this  tin  ves-  Tin  vessel 
sel  with  a  mixture  of  one  part  of  hydrogen  with  two  of  atmos-   for    ex- 
pheric  air,  and  put  a  cork  in  the  mouth  of  it.    At  its  opposite  end    ploding 
is  a  small  hole  like  a  touch  hole,  to  which  I  will  apply  a  lighted   gases. 
taper,  when  the  gases  will  explode  and  blow  the  cork  out  with 
considerable  force(44). 

Caroline.  Oh!  Well,  I  had  no  idea  of  such  a  report;  why  it 
•was  like  the  firing  of  a  gun!  Is  it  possible  that  it  was  produced 
by  the  two  gases  only  ? 

Mrs  B.  The  report  was  certainly  loud,  but  not  exactly  like  ^Jjf^  '  \ 
that  of  a  gun.  Had  we  taken  pure  oxygen,  with  a  proper  portion 
of  hydrogen,  it  would  have  been  much  louder.  Had  I  used  oxy- 
gen, however,  I  should  have  mixed  with  it  twice  its  bulk  of 
hydrogen;  but  employing  atmospheric  air  I  added  but  one  half  its 
bulk  of  hydrogen.  Can  you  tell  the  reason  of  this(45)? 

Emily.  I  think  I  can  explain  it:  there  is  so  much  nitrogen  in  atmos- 
.pherie  air,  that  half  its  bulk  of  hydrogen  is  sufficient  for  the  oxygen,  as  the 
latter  combines  with  twice  its  volume  of  the  former(46).  I  do  not  however 
understand  the  cause  of  the  explosion;  for  as  the  two  gases  unite,  and  be- 
come water,  I  should  suppose  that  instead  of  expansion,  there  would  be  a 
sudden  condensation. 

Mrs  B.  You  are  perfectly  correct  in  your  explanation,  and  your  difficulty 
will  be  easily  solved.  The  two  gases,  the  bases  of  which  unite  to  form  wa- 
ter, give  out  a  large  portion  of  their  combined  heat,  which  becoming  free, 
rarefies  the  vapour  at  the  moment  of  its  production,  and  thus  gives  rise  to 
the  explosion,  like  gunpowder  and  other  similar  compounds(47).  The  in- 
tense heat  given  out  in  this  combustion,  has,  as  you  will  hereafter  learn, 
been  employed  by  the  chemist  in  fusing  and  volatilizing  some  of  the  most 
refractory  articles. 


41.  How  is  this  phenomenon  explained? 

42.  From  what  cause  does  this  gas  kindle  with  a  slight  explosion? 

43.  What  would  result  from  a  complete  mixture? 

44.  In  what  way  may  the  gases  be  exploded? 

45.  What  volumes  of  oxygen  and  of  common  air  are  used?. 

46.  For  what  reason  is  this  difference  made? 

47".  In  what  way  isjhe  loud  explosion  accounted  for? 


ON  THE  COMPOSITION  OF  WATER. 


131 


Caroline.  Why  is  it  necessary  to  kindle  the  hydrogen  in  order  to  its 
combination  with  oxygen?  would  they  not  unite,  slowly  at  least,  by  merely 
mixing  them  together? 

Mrs  B.  Perhaps  I  cannot  satisfactorily  answer  your  question,  why  we  must 
apply  heat;  but  you  have  already  learned  that  it  is  one  of  the  most  powerful 
agents  in  producing  chemical  changes.  The  bases  of  the  two  gases  may  be 
made  to  combine  by  sudden  condensation,  whiqh  causes  the  particles  to  ap- 
proximate, and  forces  out  a  portion  of  the  heat  of  capacity;  but  this  is  no 
easy  or  safe  experiment(48). 

Emily.  By  what  means  can  we  collect  the  water  which  is  produced  by 
the  combination?  In  the  explosions  and  combustions  which  we  have  seen, 
it  is  dissipated  as  it  is  formed. 

J\Irs  3.  We  can  very  readily  show  the  actual  formation  of  Formation 
water,  by  merely  holding  a  piece  of  cold  metal  over  the  flame  of  of  -water 
burning  hydrogen:  the  "watery  vapour  will  be  condensed  upon  it,  by  burn- 
so  as  to  be  quite  apparent,  and  indeed  to  run  off  in  drops.  By  ing-  Ay- 
holding  a  cold  glass  receiver  over  the  flame,  the  vapour  of  water  drogen 
will  be  condensed  on  the  inside  of  it,  and  this  will  continue  until  •within  a 
the  receiver  itself  becomes  heated(49).  bell  glass. 

Caroline.     Yes,  indeed;  the  glass  is  now  quite  dim  with  mois-.       xSv 
ture !     How  glad  I  am  that  we  can  see  the  water  produced  by  this 
combustion. 

Emily.     It  is  exactly  what  I  was  anxious  to  see;  for  I  confess  I 
was  a  little  incredulous. 

Mrs  B.  If  I  had  not  held  the  bell  glass  over  the  flame,  the 
water  would  have  escaped  in  the  state  of  vapour,  as  it  did  in  the 
former  experiments.  We  have  here,  of  course,  obtained  but  a 
very  small  quantity  of  water;  but  the  difficulty  of  procuring  a  pro- 
per apparatus,  with  sufficient  quantities  of  gases,  and  the  length 
of  time  required  for  the  experiment,  prevent  my  showing  it  to 
I  you  on  a  larger  scale. 

The  composition  of  water  was  suspected  by  the  celebrated  Mr 
Watt,  and  was  discovered  at  about  the  same  time,  both  by  Mr 
Cavendish,  in  England,  and  by  the  celebrated  French  chemist, 
Lavoisier(SO).  The  latter  invented  a  very  perfect  and  ingenious 
apparatus,  to  effect  with  great  accuracy,  and  upon  a  large  scale, 
the  formation  of  water  by  the  combination  of  oxygen  and  hydro- 
gen gases.  Two  tubes,  conveying  due  proportions,  the  one  of  oxygen,  thfe 
other  of  hydrogen  gas,  were  inserted  at  opposite  sides  of  a  large  globe  of  glass 
previously  exhausted  of  air.  The  stream  of  hydrogen  gas  was  kindled  withift 
the  globe,  by  the  electrical  spark,  at  the  point  where  the  two  came  in  con- 
tact. They  burnt  together,  that  is  to  say,  the  hydrogen  combined  with  the 
oxygen,  the  caloric  was  set  at  liberty,  and  a  quantity  of  water  was  produced, 
exactly  equal  in  -weight  to  that  of  the  two  gases  introduced  into  the  globe. 

Caroline.  And  what  was  the  greatest  quantity  of  water  ever  formed  in 
this  apparatus? 

Mrs  B.  Several  ounces;  indeed,  very  nearly  a  pound,  if  I  recollect  right; 
but  the  operation  lasted  many  days(51). 

Emily.  This  experiment  must  have  convinced  all  the  world  of  the  truth 
of  the  discovery.  Pray,  if  improper  proportions  of  the  gases  were  mixed 
and  set  on  tire,  what  would  be  the  result? 


48.  Can  the  gases  be  made  to  explode  without  ignition? 

49.  How  can  the  formation  of  water  be  exhibited? 

50.  By  whom  was  the  composition  of  water  discovered.' 

51.  What  celebrated  experiment  is  mentioned? 


132 


CONVERSATIONS  ON  CHEMISTRY. 


Musical 
sounds 
caused    by 
the  combus- 
tion of  hy- 
drogen    in 
tubes. 


J\frs  J8.  Water  would  still  be  formed,  but  there  would  be  a  residue 
of  either  one  or  other  of  the  gases;  because,  under  these  circumstances,  hy- 
drogen and  oxygen  will  combine  only  in  the  proportions  requisite  for  the 
formation  of  water. 

One  of  the  methods  employed  to  ascertain  the  proportionate  quantity  of 
oxygen  in  the  atmosphere,  is  the  combustion  of  hydrogen  in  a  confined  por- 
tion of  it,  by  which  the  whole  of  the  oxyge^  may  be  separated,  the  nitrogen 
alone  remaining,  or  more  commonly  nitrogenjaixed  with  a  portion' of  hydro- 
gen(52).  There  are  several  other  methods  of  separating  the  oxygen  from 
the  nitrogen  of  the  atmosphere.  ^To  this  I  shall  call  your  attention  more 
particularly  when  examining  the  properties  of  phosphorus. 

Emily.  Pray  is  there  not  some  danger  of  an  explosion  from  the  acci- 
dental mixture  of  atmospheric  air  with  hydrogen,  when  we  suppose  that 
we  are  only  going  to  burn  the  latter? 

Mrs  B.  Great  caution  is  necessary  to  prevent  it.  I  have  again 
prepared  the  bottle  and  tube,  to  obtain  the  flame  of  hydrogen 
gas,  and  you  may  observe  that  I  allow  it  to  escape  for  some 
time  before  setting  fire  to  it.  1  do  this  in  order  to  be  sure  that 
all  the  atmospheric  air  is  expelled  from  the  bottle,  otherwise  it 
might  be  blown  to  pieces,  and  much  mischief  done  by  the  scat- 
tering of  its  contents(53). 

I  am  about  to  show  you  another  curious  effect  produced  by 
the  combustion  of  hydrogen  gas,  which  I  now  kindle  with  the 
taper.  I  have  here  a  glass  tube  open  at  both  ends,  which  I  place 
over  the  burning  jet. 

Enuly.  What  ft  strange  noise  it  produces,  something  like  the. 
JEolian  harp,  but  not  so  sweet. 

Caroline.  It  is  very  singular  indeed;  but  I  think  rather  too 
powerful  to  be  pleasing.  Pray  how  is  this  sound  accounted 
for(54)? 

JMrs  B.  These  musical  tones  are  considered  as  a  continued 
series  of  explosions  within  the  tube(55).  Tubes  of  various  ma- 
terials and  dimensions  produce  different  tones,  some  very  sweet, 
and  others  quite  harsh,  ana  with  a  commotion  which  not  unfre- 
quently  extinguishes  the  flame.  Tubes  of  different  materials, 
flasks,  phials,  and  hollow  globes,  may  be  tised  in  the  experi- 
ment; and  other  combustible  gases  and  vapours  answer  instead 
of  hydrogen(56). 

Caroline.  By  the  preparation  which  you  have  made  I  think 
that  we  are  now  to  see  some  of  the  fragile  air  balloons  which 
you  promised  us. 

J\frs  B.  We  shall  now  fill  some  soap  bubbles  with  hydrogen 
gas  instead  of  atmospheric  air,  and  you  will  see  with  what  ease 
and  speed  they  will  ascend,  from  the  lightness  of  the  gas. — Will 
you  mix  some  soap  and  water,  whilst  I  fill  this  bladder  with  the 
gas  contained  in  the  receiver  which  stands  on  the  shelf  in  the 
water  bath(57)> 

Caroline.  What  is  the  use  of  the  brass  stop-cocks  which 
are  attached  to  the  top  of  the  receiver? 


52.  To  what  use  is  the  combustion  of  hydrogen  applied? 

53.  What  precaution  is  necessary  when  experimenting  with  hydrogen? 

54.  How  may  musical  tones  be  produced  by  burning  it? 

55.  In  what  way  is  the  noise  accounted  for? 

56.  Is  the  effect  confined  to  hydrogen  and  to  tubes  of  glass? 

57.  What  experiment  is  mentioned  with  soap  bubbles? 


ON  THE  PROPERTIES  OF  HYDROGEN. 


133 


Apparatus  for  transferring   Gases  from  a  Receiver  into  a  Bladder,  for 
blowing  Bubbles,  or  for  other  Purposes. 


M.rs  B.  It  is  to  afford  a  passage  to  the  gas,  when  required.  There  is, 
you  see,  a  similar  stop-cock  fastened  to  this  bladder, which  is  made  to  fit  on 
the  receiver.  I  screw  them  one  on  the  other,  and  now  turn  the  two  cocks, 
to  open  a  communication  between  the  receiver  and  the  bladder;  then,  by 
sliding  the  receiver  off  the  shelf,  and  gently  sinking  it  into  the  cistern,  the 
water  rises  in  the  receiver,  and  forces  the  gas  into  the  bladder(58). 

Caroline.  Yes.  I  see  the  bladder  swell  as  the  water  rises  in  the  re- 
ceiver. 

Mrs.B.  I  think  that  we  have  already  a  sufficient  quantity  in  the  bladder 
for  our  purpose.  We  must  be  careful  to  turn  the  upper  key  before  we  sepa- 
rate the  bladder  from  the  receiver,  or  the  gas  would  escape.  Now  I  must 
fix  a  pipe  to  the  stopper  of  the  bladder,  and  by  dipping  its  mouth  into  the 
soap  and  water,  take  up  a  few  drops.  I  now  again  turn  the  cock,  and  squeeze 
the  bladder,  in  order  to  force  the  gas  into  the  soap  and  water,  at  the  month 
of  the  pipe. 

Emily.  There  is  a  bubble,  but  it  bursts  before  it  leaves  the  mouth  of 
the  pipe. 

Jlfrs  B.  We  must  have  patience  and  try  again.  It  is  not  so  easy  to  blow 
bubbles  by  means  of  a  bladder,  as  simply  with  the  breath. 

Caroline.  Now  a  bubble  ascends.  Owing  to  its  levity,  it  rises  with 
great  rapidity,  and  thus  shows  very  satisfactorily  the  nature  of  those  larger 
and  stronger  machines  which  enable  men  to  rise  above  the  clouds(59). 

Mrs  B.  We  will  now  blow  some  with  a  mixture  of  oxygen  and  hydrogen 
in  due  proportions.  These  will  not  ascend  with  quite  so  much  rapidity  as  the 
others;  but  if  you  catch  them  in  their  ascent  with  a  lighted  taper,  they  will 


58.  Describe  the  mode  of  filling  a  bladder  with  hydrogen  or  other  gas. 

59.  How  are  such  bubbles  blown,  and  what  do  they  exemplify? 


134  CONVERSATIONS  ON  CHEMISTRY. 

give  a  report  like  a  pistol(60).  I  have  now  filled  the  bladder  with  the 
mixed  gases,  and  you  must  be  careful  not  to  touch  the  bubble  before  it  has 
escaped  from  the  pipe,  or  the  whole  contents  of  the  bladder  will  explode. 
Try  it  Caroline,  but  mind  the  caution  I  have  given. 

Soap  Bubbles  blown  by  means  of  a  Bladder 


Caroline.  How  awkward  I  must  be;  three  have  escaped  and  I  havo  iwt 
been  able  to  touch  one  of  them!  If  I  do  riot  succeed  better  in  the  next  tt**\ 
I  will  hand  the  taper  to  Emily.  I  am  lucky  at  last,  and  will  not  risk  »iy 
credit  by  another  attempt.  How  powerfully  explosive  this  compound  must 
be  to  produce  so  loud  a  report  in  so  small  a  quantity  and  with  so  tain  an 
envelope ! 

Mrs  B.  Were  we  to  dip  the  bowl  of  the  pipe  into  the  vessel  of  soap- 
suds, and  continue  to  blow  until  the  bubbles  had  piled  themselves  up  on  the 
surface,  and  then  touch  them  with  a  lighted  taper,  the  explosion  would  be 
absolutely  deafening(61). 

Emily.  I  had  no  conception  that  the  subject  of  water  and  its  conatituents 
was  so  extensive  and  so  full  of  interest.  With  respect  to  its  composition, 
we  have  the  most  perfect  proof,  both  analytical  and  synthetical;  and  it 
seems  in  its  decompositions  and  recompositions  to  perform  a  very  important 
part  indeed  in  the  economy  of  nature. 

Mrs  B.  You  have  yet  but  a  very  inadequate  idea  of  its  uses  and  combi- 
nations'. There  are  but  few  compounds  into  which  water,  or  one  or  both  of  its 
constituents  does  not  enter,  and  but  few  agents  more  universally  diffused.  It 
exists  in  a  solid  state  in  most  rocks  and  stones,  in  many  instances  so  inti- 
mately combined  with  them  as  not  to  be  separated  at  a  red  heat.  Sub- 
stances with  which  it  is  thus  intimately  combined  are  called  Hydrates(62). 
Water  is  capable  of  absorbing  all  the  gases,  some  of  them  in  very  minute,  and 
others  in  very  large  proportions(63).  Water  is  a  solvent  of  more  substan- 
ces than  any  other  fluid.  Hence  we  rarely  or  never  find  it  pure  in  nature;  as 
it  dissolves  a  portion  of  many  of  the  minerals  over  which  it  passes  in  the 
bowels  of  the  earth(64).  The  catalogue  of  its  uses  would  be  almost  endless. 

Caroline.  Do  oxygen  and  hydrogen  combine  in  any  other  proportions 
than  those  which  form  water?  I  do  not  recollect  that  you  have  intimated 
to  us  that  there  is  any  such  compound. 

Mrs  B.  Until  within  a  very  few  years,  no  other  combination  of  oxygen 
and  hydrogen  was  known;  but  in  1818  Thenard,  one  of  the  most  celebrated 
chemists  of  France,  published  an  account  of  a  new  compound  which  he  had 


60.  What  variation  of  the  experiment  is  stated  ? 

61.  In  what  manner  may  a  louder  explosion  be  produced? 

62.  What  is  said  of  the  numerous  combinations  of  water? 

63.  What,  of  its  absorbent  power? 

64.  What  is  remarked  respecting  it  as  a  solvent? 


ON  SULPHUR  AND  ITS  COMBINATIONS.  135 

artificially  formed,  of  oxygen  and  hydrogen,  containing  twice  the  relative 
quantity  of  oxygen  which  exists  in  water.  This  he  called  DEUTOXIDE  OF  HY- 
DROGEN, because  it  contains  two  atoms,  or  proportionals,  of  oxygen  to 
one  of  hydrogen(65). 

It  is  a  corrosive  fluid,  much  heavier  than  water,  and  possessing  several 
very  peculiar  properties;  but  neither  these  nor  the  mode  of  its  preparation  are 
important  for  you  to  know.  When  heated  to  about  60°  it  gives  out  pure 
oxygen,  and  is  converted  into  water(66). 


CONVERSATION  XIII. 

ON  SULPHUR  AND  ITS  COMBINATIONS  WITH  OXYGEN  AND 
HYDROGEN. 

Properties  of  the  Non-metallic  Simple  Inflammables.  Natural  History  of 
Sulphur.  Sublimation.  Combustion  of  Sulphur  in  Atmospheric  Jlir.  Acid 
formed  by  its  Combustion.  Absorption  of  Gases  by  Water.  Their  Liquefac- 
tion. Bleaching.  Manufacture  of  Sulphuric  Acid.  Sulphuretted  Hydro- 
gen. Harroiogate  Waters.  Hydrosulphurets.  v  • 

Mrs  B.  The  subject  of  our  last  conversation  has  made  you  acquainted 
•with  one  of  a  class  of  bodies  sometimes  called  the  SIMPLE  INFLAMMABLES;  that 
is,  substances  which  have  never  been  decompounded, — which  are  capable  of 
combining  with  oxygen,  and  of  emitting  light  and  heat  when  the  combina- 
tion is  rapid, — and  which  form  with  it  acids  or  oxides(l). 

Having  attended  to  the  first  member- of  this  class,  hydrogen,  we  shall  take 
up  three  of  the  others  in  the  following  order:  Sulphur,  Phosphorus^  and  Car- 
bon(2);  deferring  the  remainder,  because  I  think  they  may  be  more  advanta- 
geously introduced  out  of  what  might  seem  to  be  their  regular  turn. 

Caroline.  But  I  understood  that  the  metals  were  all  inflammable,  and 
that  they  were  also  simple  bodies;  and,  beside  these,  there  are  many  other 
combustibles  which  are  not  contained  in  your  list. 

Mrs  B.  The  metals  are  certainly  simple  inflammables,  but  on  account 
of  their  distinctive  characteristics,  they  are  usually  placed  in  a  class  by 
themselves;  those  just  enumerated,  with  a  few  others,  being  frequently  de- 
nominated the  non-metallic  simple  inflammables(3}.  With  respect  to  the 
many  other  combustibles  to  which  you  allude,  they  are  compounds,  and  are 
therefore  expressly  excluded  from  the  class  in  question. 

Caroline.  I  am  glad  that  we  have  again  a  solid  body  to  examine,  one 
that  we  can  see  and  touch;  although  I  must  acknowledge  that  in  investigat- 
ing its  properties  I  do  not  anticipate  the  gratification  of  all  the  senses.  The 
smell  of  brimstone  is  to  me  one  among  the  most  offensive;  I  dislike  even  to 
light  a  match. 

Mrs  B.  Pure  sulphur  has  but  little  or  no  odour,  and  you  have  fallen  into 
the  common  error  of  confounding  the  smell  of  one  of  the  products  of  its  com- 
bustion, with  that  of  the  simple  article.  The  smell  of  a  burning  match  is 
not  the  smell  of  sulphur.  Sulphur  is  seldom  discovered  in  nature  in  a  pure 


65.  What  other  combination  is  there  of  oxygen  and  hydrogen? 

66.  What  particulars  are  stated  respecting  it? 

1.  What  properties  distinguish  the  simple  inflammables? 

2.  What  four  bodies,  belonging  to  that  class,  are  named? 

3.  How  are  they  distinguished  from  the  metals,  which  are  also  simple  in* 
flammable  s? 


136  CONVERSATIONS  ON  CHEMISTRY. 

unmixed  state(4).  So  great  is  its  affinity  for  other  substances,  that  it  is  almost 
constantly  found  combined  with  some  of  them.  It  is  most  commonly  uni- 
ted with  the  metals,  under  various  forms,  and  from  some  of  these  combina- 
tions is  separated  by  a  very  simple  process.  It  exists  likewise  in  many 
mineral  water 55  and  some  vegetables,  especially  those  of  the  cruciform  tribe, 
yield  it  in  various. proportions.  It  is  also  found  in  animal  matter 5  in  short, 
it  may  be  discovered  in  greater  or  less  quantity  in  the  mineral,  vegetable, 
and  animal  kingdoms(5). 

Emily.  I  have  understood  that  large  quantities  of  sulphur  are  found  in  the 
island  of  Sicily,  and  in  other  volcanic  countries. 

Mrs  B.  The  larger  portion  is,  I  believe,  supplied  from  Sicily,  the 
Lipari  islands,  and  some  other  parts  of  Italy,  where  it  is  found  in  abun- 
dance, and  sometimes  in  a  state  of  very  great  purity;  the  continued  inte- 
rior heat  of  the  earth  in  these  places  causing  it  to  rise  to  the  surface  by 
sublimation^}. 

Emily.     Pray,  what  is  sublimation? 

J\frs  B.  It  is  a  process  very  analogous  to  that  of  distillation.  The  differ- 
ence between  them  is,  that  in  sublimation  we  operate  upon  solids,  and 
in  distillation  upon  fluids.  There  are  several  solid  substances  which  may 
be  converted  into  vapour  by  heat,  and  which  condense  again  by  cold.  Sul- 
phur is  one  of  these,  and  advantage  is  taken  of  this  property  to  separate  it 
from  the  fixed  earthy  or  metallic  substances  with  which  it  is  commonly 
combined(7). 

Caroline.  Pray,  Mrs  B.,  what  is  the  difference  between  the  fine  powder 
which  is  called  powers  of  sulphur,  and  common  roll  brimstone. 

JUrs  B.  The  article  in  this  phial,  labelled  powers  of  sulphur,  is  sulphur 
which  has  been  sublimed,  or  volatilized  by  heat(8).  This  process  can  be 
shown,  in  the  small  way,  by  putting  some  pieces  of  sulphur  into  a  glass  flask, 
(fig.  1.)  inverting  a  second  flask  over  it,  and  applying  heat  to  the  lower  vessel. 
The  sulphur  will  then  fuse,  and  when  it  acquires  a  temperature  of  about  six 
hundred  degrees,  it  will  rise  in  vapour,  arid  be  condensed  about  the  neck 
and  body  of  the  upper  vessel(9).  In  the  large  way  the  sulphur  is  melted  in 
iron  pots,  and  ascends  in  vapour  into  a  chamber  above,  upon  the  walls  of 
which  it  is  condensed  in  the  form  of  flowers(lO).  '  You  now  perfectly  under- 
stand, I  suppose,  what  is  meant  by  sublimation? 

Emily.  I  believe  I  do.  Sublimation  appears  to  consist,  in  destroying,  by 
means  of  heat,  the  attraction  of  aggregation  of  the  particles  of  a  solid  body, 
which  are  thus  volatilized;  and  as  soon  as  they  lose  the  caloric  which  pro- 
duced that  effect,  they  are  deposited  in  the  form  of  a  fine  powder(ll). 

J\lrs  B.  In  the  case  of  sulphur  a  fine  powder  is  produced,  but  the  greater 
number  of  solids  which  undergo  sublimation,  form  in  their  condensation  a 
concrete  mass(12). 

Sulphur,  chemically  speaking,  is  exactly  the  same  substance,  whether  in 
the  form  of  lumps  or  in  powder.  For  if  this  powder  be  melted,  it  will,  in 
cooling,  be  restored  to  the  same  solid  state  in  wbjch  it  was  before  its  subli- 
mation? 


4.  Is  sulphur  often  found  in  a  state  of  purity? 

5.  With  what  different  articles  is  it  said  to  be  combined? 

6.  Whence  is  a  large  portion  of  it  obtained? 

7.  What  is  intended  by  sublimation? 

8.  What  is  the  difference  between  flowers  of  sulphur  and  roll  brimstone? 

9.  How  may  its  sublimation  be  exhibited? 

10.  How  is  it  performed  in  the  large  way? 

11.  In  what  does  the  process  appear  to  consist? 

12.  Are  sublimed  articles  generally  in  the  form  of  powder? 


ON  THE  PROPERTIES  OF  SULPHUR. 


137 


Caroline.  But  if  there  is  no  real  change  produced  by  the  sublimation  of 
the  sulphur,  what  is  the  use  of  that  operation? 

J\frs  B.  It  divides  the  sulphur  into  very  minute  parts,  in  which  state  it 
is  largely  used  in  medicine.  It  is  also  a  means  of  purification,  as  it  sepa- 
rates it  completely  from  all  earthy  and  other  fixed  substances(lS). 

Caroline.  Sublimation  appears  to  me  like  the  beginning  of  combustion, 
for  the  completion  of  which  one  circumstance  only  is  wanting,  the  absorp- 
tion of  oxygen. 


Sublimation  of  Sulphur. 


Sulphur  burnt  in  Jltmosphe- 
ric  Mr 


Fig.  1.  Fig.  2. 


Mrs  B.  But  that  circumstance  is  every  thing.  No  essential  alteration 
is  produced  in  sulphur  by  sublimation;  whilst  in  combustion  it  combines 
with  oxygen,  forms  a  new  compound,  totally  different,  in  every  res- 
pect, from  sulphur  in  its  pure  state(l4).  We  shall  now  burn  some  sulphur 
in  atmospheric  air,  in  the  same  way  in  which  we  lately  burnt  it  in  oxygen 
gas.  I  have  in  the  present  instance  (fig.  2. )  put  some  flowers  of  sulphur  into  the 
copper  spoon,  and  this  I  ignite  by  means  of  a  red  hot  wire.  As  I  place  it  in 
the  receiver,  over  water,  the  vessel  becomes  filled  with  the  same  kind  of 
dense  vapour  which  you  witnessed  in  the  former  experiment;  and  you  will 
soon  perceive  the  water  rise  in  the  receiver,  a  little  above  its  level  in  the 
plate(15). 

Emily.  The  information  which  you  gave  us  when  on  the  subject  of  oxy- 
gen, will,  I  think,  suggest  an  explanation  of  this.  The  sulphur  is  now  com- 
bining with  the  oxygen  of  the  air,  and  forming  sulphuric  acid;  which  mix- 
ing with  the  water,  causes  a  partial  vacuum  in  the- glass,  and,  of  course,  the 
pressure  of  the  atmosphere  forces  the  water  to  rise  in  the  receiver(16). 


13.  What  advantages  are  obtained  by  subliming  sulphur? 

14.  What  is  the  essential  difference  between  sublimation  and  combustion? 

15.  Describe  the  experiment  of  burning  it  in  atmospheric  air. 

16.  Why  does  the  water  rise  in  the  receiver? 

M  2 


138  CONVERSATIONS  ON  CHEMISTRY. 

Mrs  B.  You  have  made  a  very  good  attempt  at  an  explanation,  although 
it  is  not  quite  correct.  It  is  sulphurous,  and  not  sulphuric  acid  which  is 
formed(17).  SULPHUROUS  ACIB,  at  the  common  temperature  and  pressure  of 
the  atmosphere,  is  a  colourless,  invisible  gas.  When  water  is  present  it 
absorbs  this  gas  and  converts  it  into  the  liquid  form.  One  pint  of  water 
will  absorb  thirty-three  pints  of  this  gas.  It  is  readily  distinguished 
from  all  others  by  its  strong  suffocating  odour.  What  Caroline  called  the 
smell  of  brimstone,  is  the  smell  of  this  acid.  When  you  set  fire  to  the  sul- 
phur on  the  end  of  a  match,  sulphurous  acid  is  formed,  and  mixing  with  the  at- 
mosphere produces  that  offensive  smell  with  which  every  one  is  familiar(16). 

Caroline.  We  have  here,  then,  two  curious  examples  of  the  effect  of  che- 
mical combination.  The  solid  yellow  sulphur  is  converted  into  an  invisible 
gas;  and  two  bodies,  sulphur  and  oxygen,  which  in  their  separate  state  have 
no  smell,  acquire  a  most  pungent  odour. 

Emily.  Yes,  and  a  gas  by  merely  coming  in  contact  with  water,  is  ab- 
sorbed by  it  in  a  quantity  equal  to  thirty-three  times  the  bulk  of  the  water, 
and  is  thus  made  to  assume  the  liquid  form(19). 

Mrs  B.  I  am  much  pleased  with  your  reflections,  as  they  show  both  at- 
tention and  judgment.  Large  as  is  the  quantity  of  sulphurous  acid  which 
combines  with  water,  you  will  learn  that  there  are  some  other  gases  of 
which  it  absorbs  several  hundred  times  its  own  bulk.  Gases  which  have 
been  thus  absorbed,  are  expelled  again  unaltered,  by  heating  the  water(20). 
Sulphurous  acid  may  be  converted  into  the  liquid  state  either  by  pressure, 
or  by  intense  cold,  without  the  presence  of  water;  but  it  will  again  assume  the 
gaseous  form  when  the  pressure  is  removed,  or  the  temperature  raised. 
Several  of  the  gases  have  been  thus  brought  to  the  liquid  state,  although  less 
readily  than  sulphurous  acid(21 ). 

Emily.  If  this  gas  is  invisible,  what  caused  the  white  vapour  which  we 
saw  in  the  glass,  and  which  has  now  disappeared? 

Mrs  B.  This  was  caused  by  the  union  of  the  gas  with  the  watery  va- 
pour contained  in  the  glass,  and  which  is  now  completely  absorbed  by  the  wa- 
ter. In  our  experiments  you  will  frequently  witness  a  similar  appearance. 

Caroline.  It  bears  then  some  resemblance  to  the  appearance  of  steam, 
when  it  is  partially  condensed  by  the  atmosphere  as  it  issues  from  boiling  water. 

Emily.  Is  this  gas  applied  to  any  use?  It  is  so  suffocating  that  I  should 
think  it  difficult  to  employ  it. 

Mrs  B.  It  is  used  in  bleaching,  as  it  discharges  many  of  the  lighter  co- 
lours.- Straw  and  silk,  for  example,  are  both  whitened  by  it.  The  articles 
to  be  bleached  are  moistened  and  hung  up  in  a  box,  upon  the  bottom  of 
which  is  placed  a  dish  containing  sulphur;  this  is  to  be  ignited,  and  the  box 
covered  up,  when  the  moisture  absorbs  the  gas  which  acts  upon  the  articles, 
and  destroys  their  colour.  A  rough  cask,  or  packing  case,  answers  the  pur- 
pose, as  the  air  must  not  be  perfectly  excluded,  or  the  combustion  would 
cease.  The  operation  should  be  performed  out 'of  doors(22). 

Caroline.  Well,  I  declare  I  will  turn  bleacher,  and  begin  by  an  experi- 
ment upon  my  old  straw  hat.  Cannot  we  now,  Mrs  B.,  bleach  something 
by  means  of  the  acid  which  you  have  formed? 

Mrs  B.  Although  the  water  has  acquired  a  strong  smell,  its  acid  pow- 
ers are  very  feeble,  as  but  a  very  small  quantity  ot  the  gas  has  been  produ- 


17.  What  acid  is  formed  in  the  combustion  of  sulphur? 

18.  What  is  said  respecting  its  nature  and  properties? 

19.  What  does  it  exemplify  respecting  chemical  combination? 

20.  Are  any  other  gases  absorbed  by  water? 

21.  Can  any  of  them  be  rendered  liquid:  and  how? 

22.  For  what  purpose,  and  in  what  way  is  sulphurous  acid  us£d? 


ON  SULPHUROUS  AND  SULPHURIC  ACIDS.  139 

*ed.  We  however  can  readily  bleach  this  red  rose  by  holding  it  over  the  va- 
pour of  burning  sulphur.  Three  or  four  matches  held  together  will  suffice. 
I  will  light  these,  and  hold  the  rose  so  that  the  gas,  but  not  the  flame,  shall 
come  in  contact  with  its  petals(23). 

Emily.  How  rapidly  the  effect  is  produced,  and  how  beautifully  varie- 
gated the  rose  appears!  Where  the  gas  has  touched  it,  it  is  quite  white, 
whilst  the  other  parts  have  retained  their  original  colour. 

Caroline.  Whatever  beauty  it  may  have  acquired,  is  certainly  not  ac- 
companied by  any  improvement  in  its  smell. 

Mrs  JS.  Articles  bleached  by  sulphurous  acid,  soon  lose  their  unplea- 
sant odour  by  exposure  to  the  atmosphere.  Growing  flowers  may  be  thus 
bleached  without  destroying  them,  and  white  and  red  roses  be  thus  exhibit- 
ed upon  the  same  bush(24). 

Emily.  I  suppose,  Mrs  B.,  that  sulphur  burned  in  oxygen  is  converted 
into  SDLPHTJBIC  ACID;  whilst  in  atmospheric  air  it  only  obtains  oxygen 
enough  to  form  the  sulphurous? 

•Mrs  J3.  If  we  burn  sulphur  in  dry  oxygen,  we  obtain  sulphurous  acid 
only:  when  the  experiment  is  performed  over  water,  a  small  portion  of  sul- 
phuric acid  is  produced(25).  Were  we,  however, 4o  depend  upon  this  pro- 
cess for  the  production  of  sulphuric  acid,  it  would,  instead  of  one  of  the 
cheapest,  be  the  dearest  of  the  whole  class. 

Caroline.  This  acid  appears  to  be  an  agent  of  so  much  importance,  that 
I  should  like  to  know  how  it  is  obtained? 

Mrs  JB.  I  can  give  you  only  a  general  idea  of  the  processes  followed, 
but  perhaps  this  will  be  enough  to  satisfy  you.  Sulphuric  acid,  was,  until  of 
late  years,  all  obtained  from  common  copperas,  by  a  process  which  is  still 
pursued  in  Germany(26).  Copperas,  you  may  recollect,  is  the  sulphate  of 
iron  of  the  chemists,  as  it  consists  of  sulphuric  acid,  united  to  the  oxide  of 
iron.  This  salt  is  dried,  then  put  into  a  proper  retort,  in  which  it  is  heat* 
ed  red  hot.  The  sulphuric  acid  is  thus  expelled,  and  is  collected  in  a  re- 
ceiver, the  oxide  of  iron  remaining  alone  in  the  retort(27).  The  liquid 
thus  obtained  appears  of  an  oily  consistence,  and  as  the  salt  was  often  called 
green  vitriol,  the  fluid  was  denominated  oil  of  vitriol(28). 

The  largest  portion  of  this  acid  is  now  made  by  the  direct  combustion  of 
sulphur.  The  process  is  performed  in  a  chamber  lined  with  lead,  and  hav- 
ing water  on  the  floor.  The  sulphur  intended  to  be  burnt  is  mixed  with  ni- 
tre, which,  when  heated,  supplies  a  large  portion  of  oxygen,  whilst  the  at- 
mospheric air  also  aids  in  the  oxygenation.  After  the  lapse  of  many  days 
the  water  becomes  extremely  acid;  it  is  then  put  into  proper  vessels  and 
boiled.  The  water  being  more  volatile  than  the  acid,  is  evaporated,  leaving 
the  latter  in  a  state  of  concentration,  and  possessing  a  specific  gravity  nearly 
double  that  of  water(29). 

Emily.  From  what  you  have  told  us  I  should  have  supposed  that  sul- 
phurous acid  would  still  have  been  the  principal  product  of  this  combustion. 

Mrs  JB.  And  so  it  is;  but  sulphurous  acid,  exposed  to  the  action  of  air 
and  moisture,  gradually  absorbs  oxygen  from  the  former,  and  is  thus  chang- 
ed into  sulphuric  acid.  This  change  takes  place  in  the  leaden  chamber. 


23.  How  may  a  rose  be  bleached  by  sulphurous  acid  gas? 

24.  What  is  said  further  on  this  point.' 

25.  What  acid  is  formed  when  sulphur  is  burned  in  oxygen? 

26.  From  what  was  sulphuric  acid  formerly  procured? 

27.  What  is  copperas,  and  how  was  the  acid  obtained  from  it? 

28.  Why  was  sulphuric  acid  called  oil  of  vitriol? 

29.  How  is  this  acid  manufactured  by  combustion? 


140  CONVERSATIONS  ON  CHEMISTRY. 

Some  of  the  attending  circumstances  are,  however,  too  intricate  for  you  to 
understand  at  present(SO). 

Emily,     The  sulphuric  acid  in  this  bottle  has  no  smell  •whatever. 

Mrs  JB.  The  effect  of  chemical  combination  is  here  again  exemplified. 
The  materials  composing  the  sulphurous  and  sulphuric  acids  are  the  same, 
but  in  the  latter  the  quantity  of  oxygen  is  increased  one  half.  By  this  two 
remarkable  changes  are  produced;  the  stronger  acid  is  without  odour,  and 
instead  of  existing  in  the  gaseous  state,  this  liquid  acid  requires  a  tempera- 
ture of  six  hundred  degrees  to  convert  it  into  vapour(31). 

There  are  two  other  compounds  of  sulphur  and  oxygen  known  to  the  che- 
mist, each  possessing  acid  properties.  They  are  artificially  formed  by  com- 
plicated processes,  and  the  mere  fact  of  their  existence  is  enough  for  you 
to  know(32). 

Caroline.  The  Harrowgate  waters,  or  sulphur  springs,  as  they  are  some- 
times called,  I  suppose  contain  sulphur  in  solution. 

Mrs  B.  Sulphur  is  insoluble  in  water  alone,  but  you  have  seen  that  its 
combinations*with  oxygen  are  soluble.  Sulphur  combines  with  hydrogen, 
and  forms  a  gas  called  SULPHURETTED  HYDROGEsr(33).  This  gas,  like  sulphu- 
rous acid,  is  absorbed  by  water,  although  in  much  smaller  quantity.  The 
Harrowgate  waters  contain  sulphuretted  hydrogen,  and  derive  their  medi- 
cinal properties  from  its  presence(34). 

Emily.  Allow  me  to  ask  what  is  meant  by  a  sulphuret?  We  have  had 
sulphites  and  sulphates,  but  I  suppose  that  this  new  name  indicates  some 
new  combination. 

Mrs  B.     Do  you  recollect  how  the  sulphites  and  sulphates  are  formed? 

Emily.  I  think  I  do.  In  the  former,  sulphurous  acid  has  combined  with 
a  base,  and  formed  a  salt;  and  in  the  latter,  sulphuric  acid  has  entered  into  a 
similar  combination(35). 

Mrs  B.  Very  well:  both  these  names,  therefore,  show  the  presence  of 
an  acid;  but  sulphur  itself  combines  with  many  bodies  without  first  uniting 
to  oxygen,  and  the  products  are  in  this  case  called  sulphurets.  Many  of 
the  ores  of  metals  are  sulphurets:  thus  we  have  sulphuret  of  iron,  which 
consists  of  sulphur  and  iron  only,  whilst  if  oxygen  enough  were  present, 
the  sulphur  would  be  acidified,  and  a  sulphate  of  iron  formed(36).  Sul- 
phuretted hydrogen,  or  sulphuret  of  hydrogen,  means  a  combination  of  these 
two  bodies  only.  You  will  presently  learn  that  there  are  likewise 
phosphurets,  carburets,  &c. ;  the  termination  uret  being  appropriated  to  the 
combinations  of  simple  non-metallic  combustible  bodies  with  each  other, 
and  with  the  metals,  alkalies,  and  earths.  Where  a  compound  is  a  gas,  it 
is  usual  to  add  ted  to  the  termination  uret,  as  sulphuretted  hydrogen  instead 
of  sulphuret  of  hydrogen(37). 

Caroline.  I  must  confess  that  if  the  sulphuretted  hydrogen  resembles 
the  water  which  contains  it,  I  am  not  anxious  to  experiment  with  it;  al- 
though it  would  be  right  to  know  how  it  is  produced. 

Mrs  B.  It  is  certainly  a  very  offensive  gas,  having  the  odour  of  putrefy- 
ing eggs.  It  is  also  very  deleterious  when  breathed,  although  medicinal 


30.  How  does  sulphurous  become  sulphuric  acid? 

31.  What  are  their  characteristic  differences? 

32.  Are  there  any  other  combinations  of  sulphur  and  oxygen? 

33.  What  combination  does  it  form  with  hydrogen? 

34.  What  mineral  waters  contain  this  gas? 

35.  What  is  intended  by  sulphites  and  sulphates  ? 

36.  What  is  meant  by  sulphurets? 

37.  What  is  said  of  the  termination  in  uret  and  uretted? 


ON  SULPHURETTED  HYDROGEN.          141 

when  taken  into  the  stomach(38).  It  may  be  readily  obtained  from  some 
of  the  metallic  sulphurets.  If,  for  exam  -le,  instead  of  pure  iron,  we  employ 
a  compound  of  iron  and  sulphur  called  sulphuret  of  iron,  and  treat  it  with 
sulphuric  acid  and  water,  just  as  we  did  the  iron  in  preparing  hydrogen  gas, 
we  should  obtain  sulphuretted  hydrogen.  The  hydrogen  of  the  decomposed 
•water,  would,  at  the  moment  of  its  formation,  dissolve  a  portion  of  the  sul- 
phur, and  thus  become  sulphuretted.  It  may  also  be  prepared  by  heating 
sulphur  in  hydrogen  gas;  but  in  this  case  its  formation  is  less  perfect  than 
when  obtained  by  means  of  the  sulphuret  of  iron(39). 

This  gas  must  often  be  formed  spontaneously  in  the  earth,  as  the  springs 
which  contain  it  are  found  in  almost  every  country. 

Caroline.  And  could  not  such  waters  be  made  artificially  by  impregnat- 
ing common  water  with  this  gas? 

Mrs  B.  Yes;  they  can  be  so  well  imitated,  as  perfectly  to  resemble  the 
Harrowgate  waters(40). 

Emily.  In  what  way  can  the  sulphur  be  separated  from  the  hydrogen  in 
these  waters/ 

Mrs  B.  It  requires  no  effort  to  effect  this,  as  it  takes  place  spontane- 
ously. The  water  which  runs  from  these  springs  deposites  the  sulphur;  the 
hydrogen  combining  with  the  oxygen  of  the  atmosphere,  and  forming  water, 
while  the  sulphur,  being  insoluble  when  alone,  is  precipitated.  There  are 
some  runs  of  water  in  which  this  depbsite  has,  in  the  lapse  of  ages,  accu- 
mulated to  a  depth  of  two  or  three  feet.  Even  in  bottles,  when  closely 
corked,  a  portion  of  the  sulphur  will  separate  and  form  an  incrustation  on 
the  glass(4l). 

Caroline.  Sulphuretted  hydrogen  must  of  course  be  inflammable,  as 
both  the  materials  of  which  it  is  compounded  are  so;  and  the  products  of 
its  combustion  I  should  suppose  would  be  water  and  sulphuric  acid. 

Mrs  B.  You  are  nearly  correct,  but  not  quite  so:  when  this  gas  is  burned 
in  atmospheric  air,  water  and  sulphurous  acid  are  formed,  the  sulphur  and 
hydrogen  both,  as  your  remark  indicates,  uniting  with  oxygen(42). 

Sulphuretted  hydrogen  has  been,  by  some  chemists,  ranked  among  the 
acids  under  the  name  of  hydro-sulphuric  acz'd(43) 

Caroline.  That  seems  strange  indeed:  where  the  acidifying  principle, 
oxygen,  is  not  present,  itsw'ould  violate  all  the  notions  we  have  acquired,  to 
admit  that  an  acid  can  exist. 

Mrs  B.  Have  you  already  forgotten  that,  although  oxygen  is  the  most 
common  source  of  acidity,  it  is  no  longer  admitted  as  the  acidifying  princi- 
ple ?  All  the  acids  we  have  yet  spoken  of,  it  is  true,  are  formed  by  its 
union  with  a  base;  but  you  have  yet  to  learn  that  hydrogen  also  may  contri- 
bute to  the  formation  of  an  acid,  and  in  fact  that  the  term  acidifying  princi- 
ple ought  not  to  be  appropriated  to  any  body,  or  class  of  bodies;  as  acidity 
results  from  the  chemical  combination  of  different  substances,  one  of  which 
is  as  necessary  as  the  other  to  the  production  of  the  acid,  although  we 
usually  call  one  the  base,  and  the  other  the  acidifying  principle(44). 

Sulphuretted  hydrogen  has  not  a  sour  taste;  but  it  reddens  blue  vegetable 
infusions,  and  combines  with  the  alkalies  and  some  of  the  earths,  neutrali- 


38.  What  properties  does  sulphuretted  hydrogen  exhibit? 

39.  By  what  processes  may  it  be  obtained? 

40.  Can  such  waters  be  artificially  made  ? 

41.  Is  the  sulphur  readily  separated  from  the  hydrogen? 

42.  What  are  the  products  of  its  combustion  ? 

43.  What  have  some  chemists  accounted  sulphuretted  hydrogen? 

44.  What  remarks  are  made  respecting  an  acidifying  principle? 


142  CONVERSATIONS  ON  CHEMISTRY. 

zing  their  properties,  and  forming  with  them  crystallizabJe  compounds, 
analogous  to  the  salts.  These  compounds  are  called  hydro- sulphurets(b5). 

We  shall  now  dismiss  the  subject  of  sulphur;  our  next  lesson  will  be 
upon  phosphorus. 

Caroline.  I  confess  that  I  shall  be  quite  willing  to  enter  trpon  a  new 
subject;  for  although  that  of  sulphur  has  proved  much  more  interesting  than 
I  had  anticipated,  still  it  has  been  less  so  than  the  consideration  of  some  of 
the  simple  bodies  which  have  preceded  it.  \ 


CONVERSATION  XIV. 

ON  PHOSPHORUS,  AND  SOME  OF  ITS  COMBINATIONS. 

Discovery  of  Phosphorus.  Substances  in  -which  it  is  contained.  It* 
Combustion.  Phosphoric  and  Phosphorous  Acids.  Phosphuretted  Hydro- 
gen. Nascent  State  of  a  Gas.  Phosphuret  of  Lime.  Modes  of  procuring 
Phosphuretted  Hydrogen.  Eudiometry  and  Eudiometers.  Application  of 
Phosphorus  and  of  Hydrogen  to  Eudiometry. 

Mrs  JS.  PHOSPHORUS,  a  portion  of  which  you  see  covered  with  water  in 
this  phial,  is  considered  by  chemists  as  a  simple  body,  although  both  it  and 
sulphur  have  by  some  been  thought  to  contain  hydrogen;  but  the  quantity 
which  has  been  detected  in  them  is  so  small,  as  to  render  it  probable  that 
if  really  present  it  was  accidentally  so. 

Phosphorus  was  first  discovered  by  Brandt,  a  chemist  of  Hamburg,  whilst 
employed  in  researches  after  the  philosopher's  stone;  but  the  method  of  ob- 
taining it  remained  a  secret  till  it  was  a  second  time  discovered  by  Kunckle, 
in  the  year  1680(1).  Phosphorus  is  generally  moulded  into  small  sticks  of 
a  yellowish  colour.  It  has  a  consistence  resembling  bees-wax(S),  and  may 
be  readily  cut  by  a  knife. 

Caroline.  I  do  n&t  understand  in  what  the  discovery  consisted:  there 
may  be  a  secret  method  of  making  an  artificial  composition;  but  how  can 
you  talk  of  making  a  substance  which  naturally  exists? 

Mrs  B.  A  body  may  exist  in  nature,  so  closely  combined  with  other 
substances,  as  to  elude  the  observation  of  chemists,  or  to  render  it  extremely 
difficult  to  be  obtained  in  its  separate  state.  This  is  the  case  with  phosphorus, 
which  is  so  intimately  combined  with  other  bodies,  that  its  existence 
remained  unnoticed,  till  Brandt  discovered  the  means  of  obtaining  it  free 
from  other  combinations.  It  is  found  in  all  animal  substances,  and  is  now 
extracted  chiefly  from  bones  by  a  chemical  process.  Bones  consist  princi- 
pally of  lime  combined  with  an  acid  having  phosphorus  for  its  base:  they 
are  therefore  a  phosphate  oflime(3). 

Phosphorus  exists  in  minute  quantities  in  certain  plants  that  bear  a  strong 
analogy  to  animal  matter  in  their  chemical  composition. 

Emily.     But  is  it  never  found  in  its  pure  separate  state? 

Mrs  _B.  Never;  and  this  is  the  reason  why  it  remained  so  long  undis- 
covered^). 


45.  What  respecting  the  combinations  of  sulphuretted  hydrogen? 

1.  What  are  we  told  respecting  the  discovery  of  phosphorus? 

2.  What  are  its  form  and  consistence? 

3.  What  is  the  substance  from  which  it  is  usually  obtained? 

4.  Why  did  phosphorus  remain  so  long  undiscovered? 


ON  PHOSPHORUS  AND  ITS  COMBINATIONS.  143 

Phosphorus  is  eminently  combustible:  it  melts  and  takes  fire  at  a  tem- 
perature but  little  exceeding  one  hundred  degrees^  and  absorbs  in  its  com- 
bustion a  weight  of  oxygen  exceeding  its  own  nearly  one  hajf. 

Caroline.  What!  will  a  pound  of  phosphorus  consume  a  pound  and  a 
half  of  oxygen(5)? 

Mrs  B.  So  it  appears  from  accurate  experiments.  I  can  show  you 
with  what  violence  it  combines  with  oxygen,  by  burning  some  of  it  in  that 
gas.  We  must  manage  the  experiment  in  the  same  manner  as  we  did  the 
combustion  of  sulphur.  You  see  that  I  cut  the  phosphorus  under  water, 
otherwise  there  would  be  some  danger  of  its  taking  fire  by  the  friction,  and 
the  heat  of  my  fingers.  I  now  put  it  into  the  receiver,  and  kindle  it  by  means 
of  a  hot  wire. 

Phosphorus  burnt  in  Oxygen  Gfl*. 


Emily.  What  a  blaze !  I  can  hardly  look  at  it.  I  never  saw  any  thing 
so  brilliant.  Does  it  not  hurt  your  eyes,  Caroline? 

Caroline.  Yes:  but  still  I  cannot  help  looking  at  it.  A  prodigious 
quantity  of  oxygen  must,  indeed,  be  absorbed,  when  so  much  light  and  ca- 
loric are  disengaged! 

Mrs  B.  The  caloric  set  free  in  the  combustion  of  a  pound  of  phosphorus, 
would  be  sufficient  to  elevate  about  a  hundred  pounds  of  cold  water  from 
the  common  temperature  to  the  boiling  point(6). 

Emily.  And  is  the  result  of  this  combustion,  like  that  from  the  burn- 
ing of  sulphur,  an  acid? 

Mrs  B.  Yes,  PHOSPHORIC  ACID;  similar  to  that  contained  in  bones,  and 
other  parts  of  the  animal  system;  and  had  we  duly  proportioned  the  phos- 
phorus and  the  oxygen,  they  would  have  been  completely  converted  into 
phosphoric  acid,  weighing  together,  in  this  new  state,  exactly  the  sum  of 
their  weights  separately;  and,  on  account  of  the  vacuum  formed,  the  water 
•would  have  ascended  into  the  receiver,  and  filled  it  entirely.  In  this 
case,  as  in  the  combustion  of  sulphur,  the  acid  vapour  formed  is  absorbed 


5.  What  is  said  respecting  the  oxygen  absorbed  in  its  combustion  > 

6.  What,  on  the  subject  of  burning  it  in  oxygen  gas? 


144  CONVERSATIONS  ON  CHEMISTRY. 

and  condensed  in  the  water  of  the  receiver.  But  when  this  combustion  is 
performed  without  the  presence  of  water,  or  moisture,  the  acid  then  appears 
in  the  form  of  cpncrete,  whitish  flakes,  which,  however,  are  extremely  ready 
to  dissolve  upon  the  admission  of  the  least  moisture(7). 

Emily.  Does  phosphorus,  in  burning  in  atmospheric  air,  produce,  like 
sulphur,  a  weaker  sort  of  acid,  which  you  would  call  phosphorous  acid? 

Mrs  B.  No;  for  although  in  atmospheric  air  it  burns  less  rapidly  than 
in  pure  oxygen  gas,  it  is  in  both  cases  so  strongly  disposed  to  combine  with 
the  oxygen,  that  the  combustion  is  perfect,  and  the  products  similar(S). 
But  phosphorous  acid  may  be  formed  by  the  slow  combustion  of  phos- 
phorus, which  takes  place  when  it  is  simply  exposed  to  the  action  of  at- 
mospheric air,  at  the  common  temperature;  in  which  case  it  is  believed  to 
combine  with  only  half  the  quantity  of  oxygen  contained  in  phosphoric  acid(9). 
Emily.  Is  not  the  process  in  this  case  rather  an  oxidation  than  a  com- 
bustion? For  if  the  oxygen  is  too  slowly  absorbed  for  a  sensible  quantity  of 
light  and  heat  to  be  disengaged,  it  is  not  a  true  combustion. 

Mrs  B.  The  case  is  not  as  you  suppose:  a  faint  light  is  emitted,  which 
is  very  discernible  in  the  dark,  and  heat  is  evolved  sufficient  to  be  just 
sensible.  A  whitish  vapour  arises  from  this  combustion,  which,  uniting  with 
water,  condenses  into  liquid  phosphorous  acid(10). 

Emily.  I  have  seen  letters  written  and  figures  drawn  with  phosphorus, 
which  are  invisible  in  day-light,  but  may  be  seen  in  the  dark  by  their  own 
light.  They  look  as  if  they  were  written,  or  drawn,  with  fire;  yet  they  do 
not  seem  to  burn. 

Mrs  B.  But  they  do  really  burn;  for  it  is  by  their  slow  combustion 
that  the  light  is  emitted,  and  phosphorous  acid  is  the  result  of  this  combus- 
tion. A  sheet  of  thick  paper,  or  of  pasteboard,  may  be  employed  for  this  pur- 
pose; but  it  is  necessary  to  be  very  careful  in  using  the  stick  of  phosphorus, 
as  the  friction  upon  the  paper  may  set  fire  to  it,  especially  in  warm  wea» 
ther(ll). 

Emily.      Will  phosphorus,  like  sulphur,  combine  with  hydrogen  gas? 
Mrs  B.     Yes;  and  the  compound  gas  which  results  from  this  combina- 
tion produces,  as  it  burns,    a  smell  still  more  fetid  than  that  of  sulphuretted 
hydrogen:  it  is,  of  course,  called  PHOSPHURETTED  HYDROGEN^  12). 

The  phosphurettcd  hydrogen  gas  has  this  remarkable  peculiarity,  that  it 
takes  fire  spontaneously  in  the  atmosphere  at  any  temperature(13).  It  is 
probable  that  those  transient  flames  or  flashes  of  light,  which  are  sometimes 
seen  in  church-yards,  and  other  places,  and  called  by  the  vulgar  Will-ivith- 
a-Wisp,  but  more  properly,  Ignis  fatuus,  are  produced  by  a  combination  of 
hydrogen  and  phosphorus,  exhaled  in  the  putrefaction  of  animal  matter(l4). 
Caroline.  Country  people,  who  are  so  much  frightened  by  those  appear- 
ances, would  disregard  them  if  they  knew  from  what  a  simple  cause  they 
proceed.  Is  the  procuring  of  phosphuretted  hydrogen  a  difficult  process? 

Mrs  B.  No,  we  have  the  means  of  obtaining  it  very  readily;  the  only 
difficulty  is  one  which  I  am  sure  you  will  overcome,  that  of  understanding 
the  rationale  of  the  processes  by  which  it  is  formed.  We  can  procure  it  by 
several  methods;  and  I  will  show  you  three  of  them,  in  each  of  which  water  is 


7.  What  is  said  respecting  the  formation  of  phosphoric  acid? 

8.  When  burnt  in  atmospheric  air,  is  phosphorous  acid  formed? 

9.  How  is  phosphorous  acid  produced? 

10.  What  is  said  respecting  its  slow  combustion? 

11.  What,  of  writing  and  drawing  with  it? 


12.  What  "other  combination  of  phosphorus  is  noticed? 

13.  What  peculiar  property  has  phosphuretted  hydrogen  ? 
14*  For  what  appearance  is  this  thought  to  account? 


ON  PHOSPHURETTED  HYDROGEN.         145 

decomposed  in  contact  with  phosphorus,  when  the  nascent  hydrogen  combines 
with  the  phosphorus,  and  forms  the  gas  in  question. 

Emily.  Pray,  Mrs  B. ,  what  is  meant  by  nascent  hydrogen;  are  there  two 
kinds  of  hydrogen? 

Mrs  B.  I  intended  to  explain  this  term  to  you,  as  the  idea  which  it  is 
designed  to  convey  is  one  of  great  importance.  Hydrogen  exists  in  the  li- 
quid state  in  water,  and  in  the  solid  state  in  most  animal  and  vegetable,  and 
in  many  mineral  substances.  Now,  whenever  it  is  obtained  from  these,  and 
made  to  assume  the  gaseous  form,  there  must  be  a  moment  in  which  this 
transition  is  taking  place,  and  in  which  the  hydrogen  is  not  completely  ga- 
seous; at  this  moment  it  is  in  its  nascent  state.  This  word,  so  happily  applied 
by  Dr  Priestley,  is  derived  from  the  Latin  nascor,  to  be  born(15). 

When  a  body  has  assumed  the  gaseous  form,  the  repulsion  existing  among 
its  particles  will,  in  numerous  instances,  completely  counteract  its  attrac- 
tion for  bodies  to  which  it  has  an  affinity;  but  the  nascent  state  is  so  favour- 
able to  combination,  that  in  passing  through  it  many  substances  unite  which 
cannot  be  made  to  do  so  under  any  other  circumstances(16). 

You  must  familiarize  yourselves  with  this  term,  as  it  applies  not  only  to 
hydrogen,  but  to  most  other  bodies,  and  I  shall  therefore  have  frequent  oc- 
casion to  use  it. 

Caroline.  It  is  at  once  so  convenient  and  so  expressive,  that  I  am  sure 
we  shall  be  in  no  danger  of  forgetting  or  mistaking  it.  Sulphuretted  hy- 
drogen is,  undoubtedly,  thus  formed,  when  water  is  decomposed  by  means 
of  the  sulphuret  of  iron  and  sulphuric  acid. 

Mrs  B.  Yes;  and  a  still  more  striking  example  is  afforded,  by  the  com- 
bination of  the  hydrogen  of  sulphuretted  hydrogen  with  the  oxygen  of  the 
atmosphere,  when  the  Harrowgate  waters  are  exposed  to  its  action.  The  sul- 
phur I  have  told  you  separates  spontaneously;  and  the  hydrogen  being  then  in 
a  nascent  state,  combines  with  the  oxygen,  without  requiring  any  elevation 
of  temperature,  as  it  would  do  had  it  fully  assumed  the  gaseous  form(17). 

Emily.  I  wonder  that  the  phosphorus  does  not  decompose  the  water  in 
which  you  keep  it,  as  it  is  capable  of  combining  with  both  of  its  constitu- 
ents; but  I  suppose  the  attraction  of  the  oxygen  and  hydrogen  for  each  other 
is  stronger  than  their  attraction  for  the  phosphorus(lS). 

Mrs  B.  That  of  course  must  be  the  cause  of  their  remaining  together 
unchanged;  but  if  we  put  in  a  third  substance  which  shall  increase  the  ten- 
dency of  the  phosphorus  to  combine  with  one  of  the  constituents  of  water, 
the  decomposition  may  be  effected(19). 

Caroline.  Just  as  the  sulphuric  acid,  by  uniting  with  its  oxide,  enabled 
the  iron  to  decompose  the  water  when  you  obtained  hydrogen  gas(20). 

Mrs  B.  When  phosphorus  decomposes  water,  it  combines  with  both  of 
its  constituents,  forming  with  its  hydrogen  phosphuretted  hydrogen,  and 
with  its  oxygen  phosphoric  acid(21).  This,  like  other  acids,  will  unite  with 
either  of  the  alkalies  and  with  some  of  the  earths,  and  form  a  salt;  with  lime, 
for  example,  it  will  form  a  phosphate  of  lime.  In  some  of  the  processes  for 
procuring  phosphuretted  hydrogen,  this  attraction  of  lime  for  phosphoric' 
acid  may  be  so  managed  as  to  enable  us  to  effect  the  object  very  readily(22). 


15.  What  is  meant  by  the  nascent  state  of  a  gas? 

16.  What  are  we  told  respecting  its  influence  in  combination? 
t  IT.  How  does  sulphuretted  hydrogen  exemplify  this  fact? 

18.  Why  does  not  phosphorus  decompose  water? 

19.  How  may  it  be  made  to  do  so? 

20.  What  analogous  fact  is  alluded  to? 

21.  When  phosphorus  decomposes  water,  what  two  compounds  are  formed? 

22.  What  article  may  be  employed  to  facilitate  the  process? 


146  CONVERSATIONS  ON  CHEMISTRY. 

It  is  best  in  the  first  place  to  combine  the  lime  and  phosphorus  together,  so 
as  to  form  a  phosphuret  of  lime.  The  small  auburn  lumps  in  this  phial  are 
the  substance  in  question.  It  is  formed  by  causing  phosphorus,  in  vapour, 
to  pass  over  the  lime  when  heated  red  hot;  the  two  combine,  and  when  cool- 
ed the  phosphuret  must  be  kept  closely  corked  up,  or  the  moisture  of  the 
atmosphere  would  quickly  decompose  it(23). 

Entity.  And  is  it  easy  to  obtain  phosphuretted  hydrogen  by  means  of 
this  phosphuret  of  lime? 

Mrs  B.  Nothing  more  is  necessary  than  to  drop  a  lump  of  it  into  a 
glass  of  water.  Bubbles  of  the  gas  will  immediately  issue  from  it,  and  take 
fire  the  moment  they  come  in  contact  with  the  air,  as  you  perceive. 

Caroline.  Astonishing!  that  is  indeed  a  most  curious  kind  of  gas,  and 
although  I  was  looking  for  bubbles  of  fire,  they  after  all  seemed  to  surprise 
me  as  much  as  though  I  had  not  expected  them. 

Mrs  B.  I  think  that  you  will  very  readily  understand  what  is  now  tak- 
ing place  in  the  glass.  The  oxygen  of  the  water  is  attracted  by  the  phos- 
phorus, unites  with  a  portion  of  it,  and  forms  phosphoric  acid;  this  then 
combining  with  the  lime,  forms  a  phosphate  of  lime,  which  remains  in  the 
water.  The  nascent  hydrogen  at  the  same  time  dissolves  another  portion  of 
the  phosphorus,  and  forms  the  phosphuretted  hydrogen,  which,  being  a  gas, 
escapes(24). 

Entity .  I  can  trace  the  operation  perfectly;  but  had  you  not  so  clearly 
explained  to  us  the  rationale  of  the  decomposition  of  water,  and  some  analo- 
gous processes,  which  has  led  us  gradually  on,  it  would  have  appeared 
quite  complex  instead  of  natural  and  simple,  as  it  now  does. 

Mm  B.  I  have  in  this  retort  the  materials  for  procuring  the  gas,  and  by 
its  aid  we  shall  obtain  larger  bubbles,  and  exhibit  their  combustion  more  per- 
fectly than  in  the  experiment  just  shown  to  you.  To  prepare  this  apparatus 
requires  some  address;  as  the  atmospheric  air  must  be  removed  from  the 
retort,  and  its  place  supplied  by  hydrogen,  nitrogen,  or  some  gas  which  will 
not  support  combustion,  otherwise  the  bubbles  would  explode  in  the  retort 
and  blow  it  to  pieces(25).  I  have  placed  the  beak  of  the  retort,  as  usual, 
under  water,  and  the  bubbles  as  they  escape  through  it  will  be  of  conside- 
rable size. 

Entity.  I  have  not  seen  you  put  any  phosphuret  of  lime  into  the  retort; 
do  you  not  use  that  material  in  the  present  instance? 

Mrs  B.  No.  The  liquid  is  a  solution  of  potash  rendered  caustic  by 
lime,  and  there  is  in  it  a  piece  of  solid  phosphorus.  The  affinities  ex- 
erted are  similar  to  those  which  rendered  the  lime  effectual  in  the  former 
example.  I  therefore  think  that  you  will  succeed  in  an  attempt  to  explain 
the  production  of  phosphuretted 'hydrogen  by  the  mutual  reaction  of  these 
substances,  when  gently  heated  together(26). 

Emily.  It  seems  to  me  that  nothing  further  is  necessary,  in  giving  the 
explanation,  than  to  change  the  term  lime  for  that  of  potash.  The  oxygen 
df  the  water  combines  with  a  portion  of  the  phosphorus,  and  forms  an  acid, 
which,  as  it  is  produced,  unites  to  the  potash,  converting  it  into  a  phosphate. 
The  nascent  hydrogen  dissolves  another  portion  of  the  phosphorus,  and 
escapes  in  the  state  of  phosphuretted  hydrogen(27). 


23.  How  is  phosphuret  of  lime  made  ? 

24.  What  action  takes  place  between  it  and  water,  producing  phosphu- 
retted hydrogen? 

25.  When  prepared  in  a  retort,  what  precaution  is  necessary  ? 

26.  What  articles  are  put  into  the  retort  to  form  this  gas  ? 

27.  Give  the  rationale  of  this  process. 


ON  PHOSPHURETTED  HYDROGEN         147 

Caroline.  A  number  of  bubbles  have  escaped  already,  and  yet  the  gas 
has  not  inflamed,  but  only  produced  a  white  vapour. 

Emily.  I  saw  a  light  distinctly  in  the  last,  and  suppose  the  reason  of 
their  not  burning  before  was  the  mixture  of  the  phosphuretted  hydrogen 
•with  the  other  gas  contained  in  the  retort.  That  last  was  quite  bright,  and 
the  explosion  very  distinct. 

Caroline.  How  beautifully  and  rapidly  they  come  over  now,  and  what  a 
curious  circular  ring  of  smoke  is  formed  by  each,  which  enlarges  as  it  as- 
eends.  From  what  is  that  effect  produced  ? 

Generation  of  Phosphuretted  Hydrogen. 


Jdrs  B.  The  hydrogen  and  phosphorus  both  unite  with  the  oxygen 
of  the  atmosphere,  the  first  forming  water,  and  the  last  phosphoric  acid.  The 
vapour  resulting  from  the  union  of  the  two  produces  the  ring(<28). 

Emily.  I  should  expect  them  to  produce  a  vapour,  but  what  should  give 
to  this  the  form  of  a  ring  I  cannot  conceive. 

JMrs  B.  And  perhaps  I  cannot  satisfactorily  explain  it  to  you.  I  have 
supposed,  however,  that  as  the  round  bubble  rises,  its  apex  being  first  ex- 
posed to  the  atmosphere,  it  there  first  takes  fire,  which  being  rapidly  pro- 
pagated down  through  the  centre,  spreads  out  the  vapour  in  the  form  you 
see.  The  smoke  from  the  firing  of  cannon  frequently  forms  such  rings,  -and 
minute  ones  are  often  produced  by  the  sputtering  of  a  candle(29). 

Caroline.  Are  there  not  some  other  interesting  compounds  of  phosphorus 
besides  those  you  have  mentioned? 

Mrs  B.  Phosphorus  combines  with  a  great  number  of  substances,  which 
we  need  not  notice  now.  It  may  be  dissolved  in  olive  oil,  and  if  a  bottle 
half  filled  with  the  solution  be  kept  closely  corked,  it  may  be  preserved 
for  years.  Whenever  the  cork  is  withdrawn  in  the  dark,  the  upper  part  of 
the  bottle  will  become  so  luminous  as  to  show  the  time  by  a  watch.  This 
effect  arises  from  the  slow  combustion  of  the  phosphorus,  on  the  admission 
of  atmospheric  air.  The  solution  may  be  rubbed  over  the  face  and  hands 
with  perfect  safety,  and  when  seen  in  the  dark  a  curious  effect  is  produced; 
the  parts  so  rubbed  being  rendered  luminous>  whilst  every  other  object  is 
invisible(SO). 

An   extremely  combustible  compound  may  be  formed  by  the  union  of 


28.  Of  what  do  the  vapourous  rings  consist? 

29.  What  is  said  respecting  the  formation  of  these  rings? 

30.  What  is  observed  respecting  phosphorus  and  olive  oil? 


148  CONVERSATIONS  ON  CHEMISTRY. 

phosphorus  and  sulphur.  This  phosphuret  of  sulphur  is  sometimes  kept 
in  small  phials  for  the  purpose  of  lighting  matches,  as  small  portions  of  it 
will  usually  take  fire  by  mere  exposure  to  the  air.  It  however  is  a  danger- 
ous material  both  to  make  and  to  handle,  and  I  therefore  do  not  use  it(31). 

Eirily.  I  think  that  you  promised  to  show  us  another  mode  of  making 
phosphuretted  hydrogen;  if  it  is  not  difficult  we  should  be  glad  to  see  it. 

Mrs  B.  It  is  very  easy,  requiring  no  other  care  than  that  necessary  to 
avoid  the  burning  of  your  fingers  with  the  phosphorus. 

Into  this  glass  I  put  some  small  pieces  of  iron,  or  Fountain  of 
zinc,  mixed  with  minute  pieces  of  phosphorus,  and  pour  Fire. 

water  upon  them.     What  more  must  I  add  to  cause  the 
decomposition  of  the  water? 

Caroline.  Sulphuric  acid,  to  be  sure,  and  then  the  hy- 
drogen "will  escape. 

Emily.  Yes,  and  I  suppose  the  nascent  hydrogen  will 
dissolve  a  portion  of  the  phosphorus,  and  become  phos- 
phuretted. 

Mrs  JS.  Very  good.  I  now  pour  in  the  acid,  and  the 
effect  will  be  immediate(32). 

Caroline.  What  a  fountain  of  fire !  The  whole  surface 
appears  to  be  in  combustion.  I  am  glad  we  have  seen  this 
experiment  as  it  appears  less  complex  than  the  others,  and 
very  clearly  elucidates  the  formation  of  the  gas. 

EUDIOMETJIT. 

Mrs  B.  Before  finally  dismissing  the  subject  of  phosphorus,  I  will  ex- 
plain to  you  the  mode  of  using  it  for  the  purpose  of  ascertaining  the  propor- 
tionate quantity  of  oxygen  in  the  atmosphere.  The  art  of  doing  this  is 
called  EUDIOMETRY,  and  the  instruments  by  which  it  is  accomplished  Eudi- 
ometers(33).  There  are  many  methods  of  effecting  the  object  in  question, 
two  of  which  I  will  now  explain;  they  are  among  the  most  perfect,  and 
such  as  you  are  well  prepared  to  understand. 

Caroline.  I  suppose  that  in  unhealthy  situations  the  quantity  of  oxygen 
is  less  than  in  those  which  are  salubrious. 

Mrs  B.  That  is  a  very  natural  conclusion,  but  it  has  not  been  found  to 
be  correct(34).  The  matter  of  disease  and  of  contagion,  which  sometimes 
exists  in  the  atmosphere,  is  of  too  subtile  a  nature  for  us  to  detect.  We  know 
its  presence  by  its  effects,  but  it  is  a  material  foreign  to  the  air,  and  does 
not  effect  its  composition(35). 

But  to  return,  to  our  subject;  whatever  substance  will  absorb  all  the  oxy- 
gen, and  leave  the  nitrogen  in  a  confined  portion  of  atmospheric  air,  will 
serve  for  eudiometry,  provided  this  substance  does  not  itself  part  with  any 
thing  to  mix  with  the  nitrogen,  and  alter  its  volume(36). 

Caroline.  I  can  very  readily  conceive  that  phosphorus  may  be  made  to 
accomplish  this  object;  as  either  by  its  slow  or  rapid  combustion  in  a  vessel 
of  atmospheric  air,  it  would  combine  with  the  oxygen  and  leave  the  nitro- 
gen behind. 

Mrs  B.     You  have  a  correct  idea  of  its  use.     If  we  ignite  phosphorus  in 


31.  What  kind  of  compound  do  phosphorus  and  sulphur  form? 

32.  What  other  mode  is  given  for  preparing  phosphuretted  hydrogen? 

33.  What  is  meant  by  eudiometry  and  eudiometers? 

34.  Is  air  in  unhealthy  situations  deficient  in  oxygen? 

35.  What  is  said  of  the  matter  of  contagion? 

86,  What  kind  of  substances  answer  for  eudiometry  ? 


ON  EUDIOMETRY. 


149 


atmospheric  air  confined  in  a  bell  glass  over  water,  the  process  will  be 
completed  in  a  few  seconds;  as  all  the  oxygen  will  unite  with  it  and  form 
phosphoric  acid,  which  the  water  will  dissolve,  leaving  the  nitrogen(37). 
The  usual,  and  a  better,  method  is  to  confine  a  stick  of  phosphorus  in  the 
vessel  of  air,  and  allow  it  to  remain  there  two  or  three  days,  when  it  will  have 
absorbed  all  the  oxygen,  and  the  water  will  consequently  have  risen  in  the 
glass,  occupying  about  one  fifth  of  its  capacity,  (fig.  1.)  A  little  phosphorus, 
however,  is  in  either  case  dissolved  by  the  nitrogen,  adding  about  l-40th 
to  its  bulk,  for  which  an  allowance  must  be  made  when  it  is  measured(38). 

Emily.  That  is  very  readily  comprehended.  Is  the  other  method  to 
which  you  alluded  equally  simple? 

Mrs  JS.  Quite  as  much  so,  as  it  depends  upon  the  exploding  of  hydro- 
gen and  atmospheric  air  together,  and  the  consequent  formation  of  water. 

Eudiometer  by  the  slow  Combus-    Eudiometer  for  detonating  Oxygen  and 
tion  of  Phosphorus.  Hydrogen. 


Fig.  1. 


Fig  2. 


This  is  the  eudiometer  employed.  It  is  a  thick,  tall,  narrow  receiver,  or 
tube,  closed  at  top.  (Fig.  2. )  Wires  are  inserted  in  two  holes  drilled  on 
opposite  sides  near  to  the  upper  part  of  it.  The  ends  of  the  wires  within 
the  tube  approach  each  other,  but  are  not  allowed  to  touch;  and  if  an  elec- 
tric spark  be  sent  through  them,  it  will,  in  passing  from  one  to  the  other, 
set  fire  to  any  explosive  mixture  of  the  gases  which  may  be  contained 
within  it(39). 

Caroline.  The  use  of  this  instrument  scarcely  needs  further  explana- 
tion; as  when  it  contains  atmospheric  air  and  hydrogen,  an  explosion  will 
unite  the  latter  with  the  oxygen  and  form  water.  But  if  you  put  in  a  little 
too  much  hydrogen,  the  superabundant  quantity  will  remain  uncombined, 
and  increase  the  volume  of  air  which  remains,  and  defeat  the  experiment. 

JMrs  JB.  This  is  really  no  source  of  error:  we  are  careful,  in  fact,  always 
to  add  an  excess  of  hydrogen,1  in  order  to  insure  the  disappearance  of  all  the 
oxygen.  We  accurately  measure  the  volume  of  the  mixed  gases  both  before 
and  after  the  explosion,  and  thus  ascertain  what  quantity  has  disappeared; 
and  we  know  that  exactly  one-third  of  this  quantity  was  the  oxygen  con- 
tained in  the  atmospheric  air.  By  an  easy  calculation,  therefore,  we  obtain 
our  object;  for  merely  subtracting  the  volume  of  oxygen  lost  from  that  of  the 


37.  How  may  the  rapid  combustion  of  phosphorus  be  used  in  eudiometry  ? 

38.  In  what  manner  may  its  slow  combustion  be  employed? 

39.  Describe  the  eudiometer  in  which  hydrogen  is  used. 

N2 


150  CONVERSATIONS  ON  CHEMISTRY. 

atmospheric  air  employed,  gives  the  relative  quantities  of  the  oxygen  and 
nitrogen(40). 

Emily.  And  of  course,  as  you  know  how  much  hydrogen  you  put  in, 
vou  can  estimate  how  much  remains  mixed  with  the  nitrogen.  The  gradua- 
tions on  the  glass  mnst  he  very  convenient  for  this  purpose. 

J\irs  B.  You  are  correct  as  respects  the  hydrogen,  but  its  quantity  is 
not  an  element  necessary  in  the  calculation  of  the  quantity  of  oxygen.  The 
tube  is  generally  graduated;  but  sometimes  the  gases  are  measured  in  ano- 
ther very  accurately  divided,  and  kept  for  that  purpose. 

I  now  leave  you  to  reflect  upon  the  lesson  of  to-day,  and  when  we  meet 
again,  recollect  that  our  subject  is  to  be  carbon. 


CONVERSATION  XV. 

ON  CARBON  AND  ITS  COMBINATIONS  WITH  OXYGEN  AND 
HYDROGEN. 

Jlfethod  of  obtaining'  pure  Charcoal.  Common  Method  of  making  it. 
Diamond.  Newton's  Conjecture.  Insufficiency  of  JLrt  to  imitate  many 
Natural  Productions.  Charcoal  indestructible  by  Time,  and  by  Heat. 
Antiseptic.  Absorbs  Gases.  Carbonic  Acid.  Soda  Water.  Carbo- 
nates. Gaseous  Oxide  of  Carbon.  Carburetted  Hydrogen.  Obtained 
from  Ponds.  Heavy  Carburetted  Hydrogent  or  Olefiant  Gas.  JDavy's 
Safety  Lamp.  Naphtha. 

Caroline.  The  substance,  the  nature  and  properties  of  which  we  are  to 
learn  to-day,  is  quite  new  to  me;  for  although  the  name  is  famiKar  from  its 
being  applied  to  tooth  powders,  and  other  advertised  articles,  carbon  itself 
I  have  never  seen. 

J\frs  B.  CABBOST  is  a  substance  not  so  new  to  you  as  you  imagine.  It  is 
nothing  more  than  charcoal  in  a  state  of  purity,  that  is  to  say,  unmixed  with 
any  foreign  ingredients(l). 

Caroline.  But  charcoal  is  made  by  art,  Mrs  B.,  and  how  can  a  body 
consisting  of  one  simple  substance  be  fabricated? 

Jflrs  B.  You  again  confound  the  idea  of  making  a  simple  body  with  that 
of  separating  it  from  a  compound.  The  chemical  processes  by  which  a 
simple  body  is  obtained  in  a  state  of  purity,  consist  in  unmaking  the  com- 
pound in  which  it  is  contained,  in  order  to  separate  from  it  the  simple  sub- 
stance in  question.  The  method  by  which  charcoal  is  usually  obtained,  is, 
indeed,  commonly  called  making  it;  but,  upon  examination,  you  will  find 
this  process  to  consist  simply  in  separating  it  from  other  substances  with 
•which  it  is  found  combined  in  nature. 

Carbon  forms  a  considerable  part  of  many  mineral  substances,  and  also  of 
all  organized  bodies;  but  it  is  most  abundant  in  the  vegetable  creation,  and 
in  the  state  of  charcoal  it  is  chiefly  obtained  from  wood.  When  the  water 
and  other  evaporable  constituents  of  the  vegetable  matter  are  volatilized  at 
the  heat  of  ignition,  the  black,  porous,  brittle  substance  that  remains  is 
charcoal(2). 


40.  How  is  the  oxygen  calculated  when  the  eudiometer  with  hydrogen  is 
used? 

1.  What  is  intended  by  carbon? 

&  Of  what  substances  is  carbon  a  component  part? 


ON  CARBON.  151 

Caroline.  But  if  heat  be  applied  to  the  wood  in  order  to  evaporate  the 
volatile  materials,  -will  not  the  temperature  of  the  charcoal  be  raised  so  as 
to  make  it  burn;  and  if  it  combines  with  oxygen,  can  we  any  longer  call 
it  pure? 

Mrs  B.  I  was  going  to  add,  that,  in  this  operation,  the  air  must  be  ex- 
cluded. 

Caroline.     How  then  can  the  vapour  fly  off? 

Mrs  B.  In  order  to  produce  charcoal  in  its  purest  state,  the  operation 
may  be  performed  in  an  iron,  or  earthen  retort.  Heat  being  applied  to  the 
body  of  the  retort,  the  evaporable  part  of  the  wood  will  escape  through  its 
neck,  into  which  no  air  can  penetrate,  as  long  as  the  heated  vapour  conti- 
nues to  rush  out.  And  if  it  be  wished  to  collect  these  volatile  products  of 
the  wood,  this  can  easily  be  done  by  introducing  the  neck  of  the  retort  into 
the  water  bath  apparatus,  with  which  you  are  acquainted(3).  But  the  pre- 
paration of  common  charcoal,  such  as  is  used  in  kitchens  and  manufactories, 
is  performed  on  a  much  larger  scale,  and  by  an  easier  and  less  expensive 
process. 

Emily,  I  have  seen  the  process  of  making  charcoal.  The  wood  is  rang- 
ed on  the  ground  in  a  pile  of  a  pyramidical  form,  with  a  fire  underneath. 
The  whole  is  then  covered  with  clay,  a  few  holes  only  being  left  for  the  cir- 
culation of  air. 

•Mrs  B.  These  holes  are  closed  as  soon  as  the  wood  is  fairly  lighted,  so 
that  the  combustion  is  checked,  or  at  least  continues  but  in  a  very  imper- 
fect manner;  but  the  heat  produced  by  it  is  sufficient  to  evaporate  and  force 
out,  through  the  earthy  cover,  the  greater  part  of  the  volatile  principles  of 
the  wood,  although  it  cannot  reduce  it  to  ashes(4). 

Emily.     Is  pure  carbon  as  black  as  charcoal  ? 

Mrs  B.  The  purest  carbon  we  can  prepare  is  so;  but  you  must  recollect 
that  the  colour  of  an  article  is  not  a  test  of  its  purity,  as  an  alteration  in  the 
aggregation  merely  of  the  particles  may  affect  the  action  of  light  upon  it, 
and  by  this  means  alone  its  colour  may  be  changed. 

Here  is  a  form  in  which  charcoal  appears,  that  I  dare  say  will  surprise 
you.  This  ring,  which  I  wear  on  my  finger,  owes  its  brilliancy  to  a  small 
piece  of  carbon. 

Caroline.     Surely  you  are  jesting,  Mrs  B. 

Emily.     I  thought  your  ring  was  diamond. 

Mrs  B.  It  is  so.  But  diamond  is  nothing  more  than  carbon  in  a  crys- 
tallized state  and  in  its  purest  form(5). 

Emily.  That  is  astonishing.  Is  it  possible  to  see  two  things  apparently 
more  different  than  diamond  and  charcoal? 

Caroline.  It  is,  indeed,  curious  to  think  that  we  adorn  ourselves  with 
jewels  of  charcoal. 

Mrs  B.  There  are  many  other  substances,  consisting  chiefly  of  carbon, 
that  are  remarkably  white.  Cotton,  for  instance,  is  almost  wholly 
carbon(6). 

Caroline.  That,  I  own,  I  could  never  have  imagined.  But  pray,  Mrs  B., 
since  it  is  known  of  what  substance  diamond  and  cotton  are  composed,  why 
should  they  not  be  manufactured,  or  imitated,  by  some  chemical  process, 
which  would  render  them  much  cheaper,  and  more  plentiful  than  the  pre- 
sent mode  of  obtaining  them  ? 

Mrs  B.     You  might  as  well,   my  dear,  propose  that  we  should  make 


3.  How  may  the  purest  charcoal  be  obtained  from  wood? 

4.  What  is  the  common  process  of  converting  wood  into  charcoal? 

5.  What  substance  consists  of  carbon  in  a  crystallized  state? 

6.  What  vegetable  substance  is  nearly  pure  carbon? 


152  CONVERSATIONS  ON  CHEMISTRY. 

flowers  and  fruit,  nay,  perhaps,  even  animals,  by  a  chemical  process;  for  it 
is  known,  by  analysis,  of  what  these  bodies  consist.  But  you  must  not  sup- 
pose that  a  knowledge  of  the  component  parts  of  a  body  will  in  every  case 
enable  us  to  imitate  it.  It  is  much  less  difficult  to  decompose  bodies,  and 
to  discover  of  what  materials  they  are  made,  than  it  is  to  recompose  them. 
Inorganic  substances,  such  as  water,  the  oxides,  acids,  and  many  others,  ad- 
mit of  a  synthetical  as  well  as  an  analytical  proof  of  their  composition.  To 
imitate  many  of  the  more  complicated  combinations  of  nature,  even  in  the 
mineral  kingdom,  is  beyond  our  reach,  and  any  such  attempt  as  regards  or- 
ganized bodies  must  ever  prove  fruitless.  Their  formation  is  a  secret  which 
rests  with  the  Creator.  You  see,  therefore,  how  vain  it  would  be  to  en- 
deavour to  make  cotton  by  chemical  means.  But,  surely,  we  have  no  rea- 
son to  regret  our  inability  in  this  instance,  when  nature  has  so  clearly 
pointed  out  a  method  of  obtaining  it  in  perfection  and  abundance(Z). 

Caroline.  I  did  not  imagine  that  the  principle  of  life  could  be  imitated 
by  the  aid  of  chemistry?  but  it  did  not  appear  to  me  absurd  to  suppose  that 
chemists  might  accomplish  a  perfect  imitation  of  inorganic  substances. 

JMrs  B.  They  have  succeeded  in  this  point  in  a  variety  of  instances,  and, 
in  the  progress  of  science,  methods  of  producing  other  such  substances,  will 
undoubtedly  be  discovered. 

Emily.  But  diamond,  since  it  consists  of  one  simple,  unorganized  sub- 
stance, might,  one  would  think,  be  perfectly  imitable  by  art. 

J\frs  B.  It  is  sometimes  as  much  beyond  our  power  to  obtain  a  simple 
body  in  a  state  of  perfect  purity,  as  it  is  to  imitate  a  complicated  combina- 
tion :  for  the  operations  by  which  nature  separates  bodies  are  frequently  as 
inimitable  as  those  which  she  uses  for  their  combination.  We  are  ignorant 
of  the  means  which  nature  employs  to  crystallize  the  diamond  :  it  is  proba- 
bly the  work  of  ages,  to  purify,  arrange,  and  unite  the  particles  of  carbon  in 
this  form.  Some  chemists,  it  is  true,  have  actually  believed  that  they  had 
succeeded  in  crystallizing  carbon,  but  upon  careful  investigation  their  con- 
clusions have  been  found  to  be  incorrect(S). 

Caroline.  I  had  always  supposed  that  the  precious  stones,  as  they  are 
called,  were  all  composed  of  earthy  materials,  like  some  of  the  transparent 
pebbles  which  we  frequently  find. 

Mrs  B.  And,  generally  speaking,  they  are  so,  the  diamond  being  the 
only  one  of  the  class  which  is  combustible(Q).  NEWTOK,  the  accurate  ob- 
server and  close  reasoner,  who  conjectured  that  water  contained  a 
principle  which  was  inflammable,  being  led  by  the  same  reasoning  which 
guided  him  in  the  former  instance,  was  of  opinion  that  the  diamond  was  a 
material  wholly  combustible.  His  discoveries  in  optics  conducted  him  to 
this  conclusion;  and  the  fact  affords  a  most  notable  example  of  the  power- 
ful aid  which  one  department  of  science  lends  to  another,  with  which,  to 
casual  observers,  it  may  have  no  apparent  connexion(lO). 

Caroline.  Pray  what  is  the  reason  that  charcoal  burns  without  smoke, 
•whilst  a  wood  fire  smokes  so  much? 

J\frs  B.  Because,  in  the  conversion  of  wood  into  charcoal,  nearly  all  the 
volatile  particles  of  the  former  have  been  evaporated(ll). 

Caroline.  Yet  I  have  frequently  seen  charcoal  burn  with  flame  ;  therefore, 
it  must,  in  that  case,  contain  some  hydrogen. 

7.  What  remarks  are  made  on  our  power  to  form  such  substances? 

8.  What  respecting  the  artificial  production  of  diamonds? 

9.  Of  what  do  the  precious  stones  generally  consist? 

10.  What  remarkable  conjecture,  respecting  the  diamond,  was  formed  by 
Newton? 

11.  Why  is  no  smoke  produced  in  the  burning  of  charcoal? 


ON  THE  PROPERTIES  OF  CHARCOAL.  153 

Mrs  B.  You  should  recollect  that  charcoal,  especially  that  which  is  used 
for  common  purposes,  is  not  perfectly  pure.  It  generally  retains  some  por- 
tion of  the  various  other  component  parts  of  vegetables,  and  of  hydrogen 
particularly,  which  accounts  for  the  flame  in  question(12).  You,  however, 
must  not  infer  that  because  a  body  burns  with  flame  it  must  necessarily  con- 
tain hydrogen,  as  flame  is  simply  a  vapour  or  gas  undergoing  combustion. 
The  flame  of  sulphur  and  of  phosphorus  is  independent  of  hydrogen  ;  and 
although  most  of  the  gases  which  are  combustible  contain  this  principle,  it 
is  by  no  means  uniformly  present(lS). 

Emily.  Charcoal  does  not,  I  suppose,  possess  any  properties  which  ren- 
der it  interesting  in  itself,  although  from  its  being  a  component  part  of 
many  substances  in  the  animal,  vegetable,  and  mineral  kingdoms,  its  af- 
finities must  be  numerous,  and  its  chemical  history  a  very  important  one. 

Mrs  B.  Charcoal,  in  the  simple  state  in  which  we  obtain  it  from  wood, 
exhibits  some  very  remarkable  characteristics.  It  seems  that  it  i«  altogether 
indestructible  by  age;  and  it  appears  that  the  arwjients  were  aware  of  this  feet, 
as  the  piles  upon  which  the  foundation  of  the  temple  of  Ephesus  rested  had 
been  charred,  that  is,  their  surfaces  had  been  burnt  to  a  coal.  "When,  in 
modern  times,  some  of  them  were  taken  up,  the  charcoal  appeared  perfectly 
fresh,  and  even  the  original  marks  of  the  axe  were  visible,  notwithstanding 
the  ages  which  had  elapsed  since  they  were  driven  into  the  ground.  In 
Herculaneum,  the  manuscripts  and  other  articles  which  were  reduced  to 
coal  have  undergone  no  decay.  Fence  posts  are  frequently  charred  by  our 
farmers,  to  ensure  their  durability  in  the  ground(l4). 

The  most  intense  fire  also  produces  no  effect  upon  charcoal,  if  kept  from 
contact  with  air,  and  other  articles  to  which  it  has  an  affinity.  It  will, 
therefore,  remain  unconsumed  and  unaltered  in  a  furnace, under  melted  glass 
Or  gold,  for  any  length  of  time(15). 

Meat  may  be  effectually  preserved  from  putrefaction  by  covering  it  with 
the  powder  of  fresh  burnt  charcoal;  and  even  after  it  has  become  tainted, 
the  same  application  will  effectually  restore  it;  The  most  offensive  ditch 
water  may  be  rendered  perfectly  clear  and  sweet  by  filtration  through  a  stra- 
tum of  pulverized  charcoal.  Red  wines,  and  most  of  the  coloured  animal 
and  vegetable  fluids,  are  rendered  colourless  by  the  same  process,  and  in 
many  instances  their  peculiar  odours  also  disappear.  Spirituous  liquors 
which  are  still-burnt  and  otherwise  badly  flavoured,  are  frequently  purified 
in  the  same  way.  The  best  filtering  machines  used  for  filtering  water, 
owe  their  good  properties  to  the  charcoal  which  they  contain(16). 

Caroline.  These  are  remarkable  properties  indeed,  and  entirely  new  to 
us.  But  can  it  be  possible  for  carbon  to  unite  chemically  with  all  the  of- 
fensive articles  which  it  absorbs,  for  certainly  it  must  at  length  become 
saturated  ? 

Mrs  B.  This  absorption  of  a  great  variety  of  substances  by  charcoal  ap- 
pears to  depend  upon  its  mechanical  structure,  and  to  be  independent,  or 
nearly  so,  of  chemical  affinity;  as  there  is  no  evidence  that  any  chemical 
combination  is  effected.  After  awhile  the  charcoal  becomes  saturated,  and 
its  power  of  absorption  ceases,  but  upon  heating  it  to  redness,  it  again  acts 
with  the  same  energy  as  atfirst(17). 

A  still  more  remarkable  action  is  exerted  between  charcoal  and  many  of 


12.  What  causes  charcoal  sometimes  to  burn  with  flame? 

13.  Is  hydrogen  necessary  to  the  production  of  flame? 

14.  What  proofs  are  given  that  charcoal  is  indestructible  by  age? 

15.  What  effect  has  heat  upon  it,  when  air  is  excluded? 

16.  What  are  its  anti-putrescent  properties? 

17.  Does  this  property  appear  to  be  a  chemical  one? 


154  CONVERSATIONS  ON  CHEMISTRY. 

,i 

the  gases.  A  lump  of  compact  well  burnt  charcoal,  will  absorb,  and  retain 
•within  its  pores,  an  astonishing  quantity  of  several  of  them.  In  one  in- 
stance the  charcoal  will  absorb  ninety  times  its  own  volume,  that  is,  a  cubic 
inch  of  the  coal  will  absorb  ninety  cubic  inches  of  the  gas$  and  there  are 
several,  the  absorption  of  which  amounts  to  thirty  volumes.  Upon  heating 
the  cbarcoal,  these  gases  are  all  given  out  again  unchanged(  18). 

Emily.  That  indeed  is  a  curious  fact.  Then,  however  pure  charcoal 
may  be  when  it  is  first  burnt,  it  cannot  long  remain  so  if  exposed  to  the  at- 
mosphere, as  it  will  absorb  a  portion  of  whatever  it  finds  there.  ,But  why 
charcoal  should  not  change  like  other  matter,  and  be  decomposed  by 
the  action  of  air,  of  moisture,  and  of  heat,  is,  I  think,  quite  unaccoun- 
table. 

Caroline.  You  forget,  Emily,  that  it  is  a  simple  body,  and  therefore  not 
liable  to  decomposition(lQ);  but  whilst  its  affinities  are  so  numerous,  I  am 
as  much  puzzled  as  you  are  to  tell  why  it  should  remain  permanent  when 
buried  in  the  earth,  or  ignited  in  the  fire. 

J[frs  B.  Carbon  in  the  form  of  charcoal  is  permanent  in  the  earth,  or 
when  exposed  to  the  air,  at  common  temperatures,  because,  in  general,  it 
requires  the  heat  of  ignition  to  cause  it  to  enter  into  combination  with  other 
substances.  It  is  permanent  in  the  fire  only  when  kept  from  contact  with 
those  agents  to  which  it  has  an  affinity,  it  not  being  volatilized  by  heat(20). 
There  are  few  bodies,  however,  which  combine  chemically,  and  manifest 
their  attractions  more  readily  than  carbon  when  at  a  red  heat. 

Caroline.  When  charcoal  is  burnt,  pray  what  becomes  of  the  carbon 
itself  during  its  combustion? 

Mrs  B.  It  gradually  combines  with  the  oxygen  of  the  atmosphere,  in 
the  same  way  as  do  sulphur  and  phosphorus,  and,  like  those  substances,  it 
is  converted  into  a  peculiar  acid,  which  flies  off  in  a  gaseous  form.  There 
is  this  difference  between  them,  however,  that  the  acid  is  not,  in  the  case  of 
carbon,  as  in  the  two  just  mentioned,  a  mere  condensable  vapour,  but  a  per  • 
manently  elastic  fluid,  which  always  remains  in  the  state  of  gas,  under 
any  ordinary  pressure  and  at  any  natural  temperature(Sl).  It  may,  however, 
be  reduced  to  the  Ijquid  state  by  strong  mechanical  pressure,  especially 
when  aided  by  a  reduction  of  temperature.  The  nature  of  this  acid  was 
first  ascertained  by  Dr  Black,  of  Edinburgh;  and  before  the  introduction  of 
the  new  nomenclature  it  was  called  fixed  air.  It  is  now  distinguished  by 
the  more  appropriate  name  of  carbonic  a«'d(22). 

Emily.  Carbon,  then,  can  be  volatilized  by  burning,  though  by  heat 
alone,  no  such  effect  is  produced? 

Mrs  B.  Yes;  but  when  so  it  is  no  longer  simple  carbon,  but  an  acid  of 
•which  carbon  forms  the  basis.  In  this  state,  carbon  retains  no  more  ap- 
pearance of  solidity  or  corporeal  form  than  the  basis  of  any  other  gas.  You 
may,  I  think,  from  this  instance,  derive  a  very  clear  idea  of  the  bases  of 
oxygen,  hydrogen,  and  nitrogen  gases,  the  existence  of  which,  as  real  bodies, 
you  seemed  almost  to  doubt,  because  they  were  not  to  be  obtained  simply 
in  a  solid  form. 

Emily.  That  is  true;  we  may  conceive  the  bases  of  oxygen  gas,  and  of 
other  gases,  to  be  solid,  heavy  substances,  like  carbon;  but  so  much  ex- 
panded by  their  combination  with  caloric  as  to  become  invisible(23). 


18.  What  is  said  respecting  its  power  of  absorbing  gases? 

19.  Why  is  not  charcoal  capable  of  decomposition? 

20.  What  is  observed  respecting  the  permanence  of  charcoal? 

21.  Into  what  is  carbon  converted  by  combustion? 

22.  Who  discovered  this  gas,  and  what  names  has  it  received? 

23.  What  illustration  respecting  others  does  this  gas  afford? 


ON  CARBONIC  ACID.  155 

Caroline.     But  does  not  the  carbonic  acid  gas  partake  of  the  blackness  of 
!  charcoal? 

Mrs  B.  Not  in  the  least.  Blackness,  you  know,  does  not  appear  to  be 
essential  to  carbon,  and  it  is  pure  carbon,  and  not  charcoal,  that  we  must 
consider  as  the  basis  of  carbonic  acid.  We  shall  make  some  carbonic  acid, 
and,  in  order  to  show  its  composition,  shall  burn  a  portion  of  carbon  in 
oxygen  gas. 

Emily.     But  do  you  mean,  then,  to  burn  diamond? 

Mrs  B.  Charcoal  will  answer  the  purpose  still  better,  being  softer  and 
more  easy  to  inflame.  Besides,  the  experiments  on  diamond  are  rather  ex- 
pensive. 

Caroline.     But  is  it  possible  to  burn  diamond? 

Mrs  B.  Yes,  it  is;  and  in  order  to  effect  this  combustion,  nothing  more 
is  required  than  to  confine  it  in  oxygen  gas,  and  to  apply  a  sufficient  degree 
of  heat.  It  was  by  burning  diamond  that  its  chemical  nature  was  ascertained. 
Lavoisier  first  proved  that  it  contained  carbon,  by  confining  it  in  this  way, 
and  heating  it  by  a  powerful  burning-glass,  by  which  process  he  obtained 
carbonic  acid(24).  With  the  exception  of  a  very  minute  quantity  of  water 
•which  is  produced  when  common  charcoal  is  burnt,  it  has  been  found  that 
there  is  no  chemical  difference  between  it  and  the  diamond;  the  same  quan- 
tity of  oxygen  combining  with  the  same  weight  of  either,  and  producing 
equal  portions  of  carbonic  acid,  which  is  the  only  product  of  the  combustion* 
On  ascertaining  the  weight  of  the  gas,  it  is  found  to  be  equal  to  that  of  the 
oxygen  and  carbon  before  the  combustion.  One  hundred  parts,  by  weight, 
of  carbonic  acid,  contain  about  twenty-eight  of  carbon,  and  seventy-two  of 
oxygen(25). 

'  We  will  now  set  fire  to  this  piece  of  charcoal,  and  suspend  it  in  areceirer 
filled  with  oxygen  gas,  and  although  we  cannot  now  take  time  to  weigh  or 
measure  the  materials,  we  shall  find  that  after  the  process  is  completed,  the 
oxygen  will  have  lost  its  power  of  supporting  combustion. 

Emily.  I  am  surprised  that  the  combustion  of  carbon  is  not  more  bril- 
liant; it  does  not  give  out  near  so  much  light  or  caloric  as  phosphorus,  or 
sulphur.  Yet  since  it  combines  with  so  much  oxygen,  why  is  not  a  pro- 
portionate quantity  of  light  and  heat  disengaged(26)7 

Mrs  B.  The  quantity  of  light  and  heat  disengaged  does  not  depend  solely 
upon  the  quantity  of  oxygen  which  enters  into  combination,  but  also  upon 
the  peculiar  nature  of  the  combustible,  and  of  the  product  of  combustion. 
Hydrogen,  when  burnt,  exhibits  but  a  feeble  flame,  yet  it  combines  with 
eight  times  its  weight  of  oxygen  in  passing  into  the  state  of  water;  and  al- 
though the  light  is  feeble,  the  heat  is  intense.  You  must  not  therefore  expect 
to  find  the  light  and  heat  disengaged  in  combustion,  to  be  in  exact  propor- 
tion to  the  oxygen  absorbed.  And  in  the  combustion  of  charcoal,  since,  in- 
stead of  entering  into  a  solid  or  liquid  combination,  as  it  does  in  the  phos- 
phoric and  sulphuric  acids,  the  oxygen  is  employed  in  forming  another 
elastic  fluid,  it  parts  with  less  of  its  caloric  than  when  uniting  to  either  of 
the  former  substances,  the  capacity  of  the  carbonic  acid  gas  produced  being 
greater  than  that  of  a  liquid  or  solid(27). 

Caroline.  But  why  should  the  water  rise  in  the  receiver  after  the  com- 
bustion  of  carbjon,  since  the  gas  within  it  retains  its  aeriform  state? 

Mrs  B.  Because  the  carbonic  acid  gas  is  gradually  absorbed  by  the 
water;  and  this  effect  would  be  promoted  by  shaking  the  receiver(28). 


24.  How  may  the  diamond  be  burned,  and  what  is  then  produced? 

25.  What  evinces  the  similarity  between  charcoal  and  the  diamond? 

26.  What  is  said  respecting  the  burning  of  charcoal  in  oxygen? 

27.  What  influences  the  amount  of  light  and  heat  in  combustion? 

28.  What  effect  has  water  on  carbonic  acid  gas? 


156  CONVERSATIONS  ON  CHEMISTRY. 

Emily.  Then  the  wMer,  I  suppose,  acquires  a  sour  taste,  and  exhibits 
the  other  properties  of  an  acid. 

Mrs  B.  The  quantity  absorbed  in  this  way  would  be  too  small  to  produce 
a  very  sensible  effect,  but  by  means  of  agitation  and  pressure  a  very  large 
quantity  may  be  forced  in.  What  is  usually  sold  under  the  name  of  soda 
water,  but  more  properly  called  Seltzer  water,  contains  nothing  but  carbon- 
ic acid,  condensed  by  suitable  machinery.  Soda  was  formerly  added,  but 
is  now  usually  omitted(29). 

Caroline.  Then  the  sparkling  appearance  and  pungent  taste  of  this 
water  are  produced  by  the  carbonic  acid  gas? 

Mrs  B.  They  are;  and  other  sparkling  liquors  derive  this  property  from 
the  same  source.  Carbonic  acid,  or  fixed  air,  is  disengaged  from  all  vinous 
liquors  when  fermenting.  Champaign,  cider,  porter,  and  many  others  fer- 
ment in  the  bottles,  which  being  closely  stopped,  retain  the  gas  until  the 
corks  are  drawn(.SO).  In  the  preparing  of  soda  water  for  sale,  the  manu- 
facturers use  very  strong  vessels  of  copper,  bound  round  with  iron;  and,  by 
means  of  forcing  pumps,  the  water  is  made  to  absorb  a1  quantity  of  carbonic 
acid  equal  to  five  or  six  times  its  own  bulk.  Such  is  the  elastic  power  of 
the  gas  when  thus  condensed,  that  notwithstanding  the  strength  of  the  ves- 
sels, they  not  unfrequently  burst;  and  their  separated  parts  have  been  pro- 
jected with  a  force,  which  has  not  only  destroyed  the  lives  of  persons  em- 
ployed iu  charging  them,  but  in  some  instances  have  made  deep  indentations 
even  in  brick  walls. 

Caroline.  It  is  not  surprising,  therefore,  that  the  water  should  be  so 
very  effervescent  and  sparkling  when  it  escapes  from  the  vessel  into  a  tum- 
bler; nor  is  it  very  remarkable  that  glass  bottles  should  burst,  when  they 
contain  within  themselves  a  manufactory  of  carbonic  acid. 

Emily.  There  must  be  some  other  method  of  obtaining  carbonic  acid  fop  ; 
impregnating  soda  water  than  that  of  burning  charcoal  in  oxygen,  or  it  1 
would  be  a  beverage  of  difficult  manufacture,  and  of  no  small  cost. 

Mrs  B.  Carbonic  acid,  by  its  union  with  the  alkalies,  some  of  the  earths,  ' 
and  other  metallic  oxides,  forms  a  class  of  saline  bodies,  which  are,  of  I 
course,  called  carbonates.  Nature  furnishes  these  carbonates  in  great  ; 
abundance,  and  by  decomposing  them  we  may  obtain  carbonic  acid.  Mar-  \ 
ble,  common  limestone,  and  chalk,  are  all  different  forms  of  carbonate  of  j 
lime,  and  some  one  of  these  may  be  procured  almost  every  where.  The  j 
carbonic  acid  may  be  expelled  from  them  by  nearly  every  other  acid.  We  \ 
generally  employ  the  sulphuric  on  account  of  its  cheapness,  and  not  because 
it  is  better  adapted  to  the  purpose  than  some  others(Sl). 

Caroline.     I  remember  seeing  a  mineralogist,  who,  in  order  to  ascertain 
whether  a  specimen  which  he  had  was  limestone,  dropped  upon  it   some 
acid,  probably  the  sulphuric,  and  an  effervescence  immediately  took  place,    j 
the  whole  surface  where  the  acid  touched  being  covered  with  minute  bubbles.    \ 

Mrs  B.     And  those  bubbles  were  undoubtedly  carbonic  acid.     I  have   ! 
here  some  pulverized  marble  which  I  will  put  into  a  retort,  and  pour  upon  I 
it  some  dilute  sulphuric  acid.    This  will  combine  with  the  lime  and  form  with  \ 
it  a  sulphate  of  lime;  while  the  carbonic  acid  gas  being  thus  set  free  from  its 
combination,  will  escape  in  torrents.     It  is  by  a  process  similar  to  this  that 
the  soda  water  manufacturers  obtain  it. 

Emily.  How  rapidly  it  comes  over?  the  receiver  is  already  filled,  and 
the  gas  wasting.  But  it  is  procured  so  easily  that  the  loss  of  a  little  is  not 
of  much  consequence. 


29.  Of  what  does  soda  water  consist? 

30.  What  is  observed  respecting  sparkling  liquors  generally? 

31.  With  what  substances  is  carbonic  acid  naturally  combined? 


ON  CARBONIC  ACID. 


157 


Nootlfs  Apparatus. 


Mrs  J3.  Before  the  soda  and  Seltzer  waters 
•were  manufactured  in  the  large  way,  and  introduc- 
ed as  common  beverages,  an  elegant  instrument, 
called  Nooth's  apparatus,  was  used  for  impreg- 
nating water  with  carbonic  acid.  This  is  the  in- 
strument upon  the  table.  The  lower  vessel  [A] 
contains  some  pulverized  marble.  The  middle 
vessel  [B]  holds  the  water  which  is  to  be  impreg- 
nated. The  upper  vessel  [C]  receives  a  portion 
of  the  water,  when  its  surface  is  pressed  upon  by 
the  gas,  thus  producing  a  reaction  which  promotes 
the  absorption.  These  vessels  fit  into  each  other 
air-tight,  and  between  the  two  lowest  is  a  valve 
[a]  which  allows  the  gas  to  pass  through  it  into 
the  water,  but  prevents  that  from  descending. 
In  the  lower  vessel  is  an  opening  [6]  to  allow  the 
diluted  sulphuric  acid  to  be  poured  upon  the  mar- 
ble. A  tube  [c]  from  the  upper  vessel  dips  into 
the^vater  to  conduct  it  up  into  the  vessel  [C].  The 
water,  when  impregnated,  is  drawn  off  at  the  vent 
[D](32). 

Caroline.  That  is,  indeed,  an  elegant  mode  of 
exhibiting  the  impregnation  of  water  with  carbonic  acid.  I  am  surprised, 
however,  at  the  freedom  with  which  this  water  is  used,  as  I  had  always  un- 
derstood that  fixed  air  was  very  poisonous.  This,  however,  must  be  an  error, 
or  it  would  not  be  thus  drank  with  impunity. 

Mrs  B.  When  taken  into  the  lungs  in  considerable  quantities,  it  instan- 
taneously destroys  life;  but  though  so  prejudicial  when  breathed,  it  is  very 
agreeable  and  salutary  to  the  stomach.  These  two  organs  are  formed  for 
very  different  purposes,  and  must  be  treated  according  to  the  functions 
which  nature  has  intended  them  to  perform(33).  All  animals  die  in  carbon- 
ic acid.  A  mouse  placed  in  a  jar  of  it 
will  expire  in  a  few  seconds.  I  am  sure, 
however,  that  you  would  rather  be  inform- 
ed of  this  fact  than  have  the  proof  of  it  exhi- 
bited to  you.  This  gas  also  immediately  ex- 
tinguishes a  taper,  or  any  other  burning 
body(34). 

Emily.  Yet  it  contains  a  large  quantity 
of  oxygen. 

Caroline.  And  so  does  water;  but  it  is 
already  combined  with  a  combustible,  and 
therefore  cannot  support  combustion. 

Emily.  You  are  rather  rapid,  my  dear 
Caroline;  I  was  just  going  to  offer  an  ex- 
planation of  the  same  kind  myself. 

Caroline.  I  beg  your  pardon,  I  know  I 
was  a  little  too  quick,  but  was  unwilling  to 
forego  the  expression  of  a  bright  thought. 

Mrs  B.  I  will  now  collect  a  quantity  of  I 
carbonic  acid,  without  using  the  pneumatic 


Carbonic  Acid  collected  in  an 
open  Vessel. 


32.  How  is  carbonic  acid  usually  obtained,  and  what  is  the  construction 
of  Nooth's  apparatus  for  impregnating  water  with  it? 

33.  What  is  remarked  respecting  its  poisonous  properties? 

34.  Will  carbonic  acid  support  life,  or  combustion? 


158  CONVERSATIONS  ON  CHEMISTRY. 

cistern,  and  will  exhibit  to  you  some  of  its  properties.  Into  the  neck  of 
this  flask,  which  contains  the  ingredients  for  making  the  gas,  I  insert  one 
end  of  a  tube,  which  is  made  to  pass  through  a  perforated  cork.  The 
tube,  as  you  see,  is  bent  twice  at  right  angles,  so  that  the  other  end  may 
descend  into  an  open  mouthed  glass.  The  gas,  as  it  escapes,  will  be  col- 
lected, fill  the  glass,  and  then  run  over  the  top(35). 

Caroline.  Why,  Mrs  B. ,  you  speak  of  it  as  though  it  were  a  liquid  instead 
of  a  gas,  and  collect  it  as  you  would  water  from  a  pump. 

Mrs  B.  It  is  half  as  heavy  again  as  atmospheric  air,  and  this  spe» 
cific  gravity  will  enable  us  not  only  to  collect  it  readily  in  this  way,  but 
actually  to  pour  it  from  one  vessel  into  another.  By  the  aid  of  a  little 
vapour  which  accompanies  the  gas,  you  may  now  see  it  running  over,  and 
descending  below  the  edge  of  the  glass(36).  This  lighted  taper  will  be  as 
completely  extinguished  the  moment  it  touches  the  gas,  as  it  would  by  im- 
mersion in  water. 

Emily.  The  smoke  from  the  taper  seems  to  have  mixed  with  the  gas  at 
the  surface,  and  forms  a  curious  kind  of  little  cleud. 

Mrs  B.  By  extinguishing  a  piece  of  burning  paper  in  the  same  way,  a 
large  quantity  of  smoke  will  be  entangled  by  the  gas,  and  render  the  motion 
of  it  visible  when  I  move  the  glass. 

Caroline.  That,  I  declare,  is  almost  seeing  the  gas  itself.  As  you 
move  the  glass  backward  and  forward,  the  surface  appears  to  be  agitated 
like  water  in  a  high  wind(37). 

Mrs  B.  I  now  place  a  burning  taper  at  the  bottom  of  another  glass,  and 
by  gently  tilting  that  which  contains  the  carbonic  acid,  as  though  we  were 
pouring  a  liquid  upon  the  taper,  the  gas  will  run  out,  and  the  taper  be  ex- 
tinguished^). 

Emily.  It  no  longer  appears  surprising  that  men  lose  their  fives  by  des- 
cending into  wells  containing  fixed  air;  and  the  importance  of  the  precau- 
tion, which  I  have  often  seen  published,  of  first  letting  down  a  lighted  candle, 
is  clearly  manifest. 

Caroline.  The  cause  of  such  accidents  is  now  perfectly  plain,  and  I 
also  perceive  the  source  of  the  danger  of  burning  charcoal  in  close  rooms: 
the  oxygen  unites  with  the  carbon,  and  produces  a  gas  which  will  destroy 
life.  What  numbers  might  have  been  saved  by  a  little  knowledge  of  che- 
mistry(39)! 

Mrs  B.  There  are  many  natural  processes  by  which  carbonic  acid  is 
produced,  and  you  ought  also  to  be  informed  that  it  is  always  contained 
in  the  atmosphere,  although  in  very  minute  quantities:  it  has  been  found 
even  on  the  tops  of  the  highest  mountains(40). 

Emily.  I  wonder  much  at  that.  From  its  weight  it  might  be  expected 
to  exist  in  low  situations;  but  I  should  have  supposed  that  if  produced  upon 
the  mountains,  its  gravity  would  carry  it  down  into  the  vallies. 

Mrs  B.  Your  idea  is  certainly  a  very  natural  one,  but  the  law  which 
governs  other  bodies  in  this  particular  does  not  apply  to  gases:  when  they 
have  once  become  mixed,  the  repulsion  of  their  particles  seems  to  prevent 
their  gravitating  among  each  other.  I  cannot  fully  enter  into  this  point, 
and  you  must  be  content  with  the  information  that  we  have  no  evidence 


35.  How  may  it  be  collected  in  an  open  glass? 

36.  What  is  observed  respecting  its  weight? 

37.  How  may  the  motion  of  this  gas  be  rendered  visible? 

38.  State  the  experiment  of  pouring  out  carbonic  acid. 

39.  What  is  said  of  fixed  air  in  wells  and  in  rooms? 

40.  What  is  said  respecting  its  presence  in  the  atmosphere? 


ON  THE  GASEOUS  OXIDE  OF  CARBON.  159 

•whatever  that  two  gases  will  separate  merely  from  a  difference  in  their 
specific  gravities(4l). 

Caroline.  You  have  not  said  any  thing  about  carbonous  acid,  as  you  did 
of  sulphurous  and  phosphorous.  I  suppose  therefore  that  it  does  not  exist. 

•Mrs  JB.  There  are  several  bases  with  which  oxygen  forms  but  one  acid, 
and  such  an  acid  always  has  its  termination  in  ic:  this  is  the  case  with  car- 
bon. It,  however,  forms  an  oxide  by  combining  with  less  oxygen  than  is 
contained  in  carbonic  acid;  this  oxide  is  a  gas,  and  is  called  carbonic  oxide, 
or  gaseous  oxide  of  car6on(42).  It  contains  but  half  the  proportionate  quan- 
tity of  oxygen  fount!  in  carbonic  acid.  It  is  inflammable,  and  I  think  that 
you  will  be  able,  without  difficulty,  to  tell  me  what  is  the  product  of  its  com- 
bustion. 

Emily.  It  must  certainly  be  carbonic  acid,  as  in  burning  it  must  unite 
with  another  portion  of  oxygen(43).  This  is  an  inflammable  gas,  not  con- 
taining any  hydrogen,  such  as  you  told  us  we  should  sometimes  meet  with. 

•Mrs  B.  Yes,  and  its  history  is  a  very  curious  one,  as  chemists  had  pro- 
cured and  experimented  with  it  for  a  considerable  period  before  its  compo- 
sition was  detected.  From  its  appearance  in  burning  they  took  it  for  granted 
that  it  contained  hydrogen;  but  as  no  water  was  produced  by  its  combustion, 
the  other  evidences  of  the  composition  of  that  fluid  were  rendered  doubtful. 
Few  things,  therefore,  could  have  gratified  the  friends  of  what  was  then 
called  the  modern  system,  more  than  the  discovery  made  by  Mr  Cruik- 
shanks,  of  England,  that  the  oxide  of  carbon  was  a  new  species  of  gas,  con- 
taining nothing  but  carbon  and  oxygen(44). 

Caroline.  This  gas  seems  to  be  half  burnt  charcoal.  Can  you  enable  us 
to  understand  any  process  by  which  it  can  be  obtained? 

Mrs  B.  Yes,  perfectly,  I  think;  there  are  several  such  processes,  but 
at  present  one  must  suffice.  If  clean  iron  filings  be  heated  to  redness  in  a 
tube,  and  carbonic  acid  be  made  to  pass  through  them,  the  filings  will  be- 
come oxidized  by  depriving  the  acid  of  a  portion  of  its  oxygen,  and  thus 
reduce  it  to  the  state  of  an  oxide.  The  carbon  is,  as  you  would  say,  in  this 
ease,  half  unburnt(45). 

Emily.  I  suppose  that  the  class  of  carbonates  and  that  of  carburets  are 
both  numerous,  as  carbon  and  its  acid  are  so  extensively  diffused. 

Mrs  B.  Carbonic  acid,  as  I  have  already  remarked,  combines  with  the 
alkalies,  with  several  of  the  earths,  and  with  the  oxides  of  some  of  the  me- 
tils.  With  carbonate  of  lime  you  have  formed  some  acquaintance,  as  we 
have  just  been  using  it.  Many  of  its  other  combinations  will  soon  be  men- 
tioned; but  I  shall  occupy  the  remainder  of  our  time  to  day  with  the  inter- 
esting class  of  carburets,  and  principally  with  the  gases  denominated  light 
and  heavy  carburetted  hydrogen. 

Caroline.  Carburetted  hydrogen,  like  sulphuretted  and  phosphuretted 
hydrogen,  must  be  very  combustible,  as  both  its  ingredients  are  so.  Have 
you  any  prepared,  or  is  it  easily  made?  I  should  like  exceedingly  to  see 
it  burnt. 

Mrs  B.  This  high  gratification  you  enjoy  every  day  and  night  of  your 
life.  The  flame  of  our  fires,  of  our  lamps  and  candles,  and  the  celebrated 
gas  lights,  are  all  examples  of  its  combustion(46).  Carbon  and  hydrogen, 
you  already  know,  are  constituents  of  nearly  all  animal  and  vegetable  sub- 
stances; but  the  resins,  oils,  and  fats  consist  in  great  part  of  these  two  ma- 


41.  What  observations  are  made  on  mixed  gases? 

42.  Does  any  gas  but  carbonic  acid  consist  of  carbon  and  oxygen? 

43.  What  are  its  properties,  and  what  the  product  of  its  combustion? 

44.  What  is  the  history  of  its  discovery? 

45.  By  what  process  may  carbonic  oxide  be  obtained? 

46.  What  is  said  respecting  carburetted  hydrogen? 


160  CONVERSATIONS  ON  CHEMISTRY. 

terials.     Whenever  such  suhstances  are  decomposed,  either  spontaneously 
or  by  the  application  of  artificial  heat,  a  new  combination  of  their  consti 
tuents  takes  place,  and  carburetted  hydrogen  isformed(47). 

•Emily.  That  explains  the  nature  of  flame  very  satisfactorily,  as  it  con- 
sists of  a  gas  undergoing  combustion;  but  I  do  not  see  why  a  gas  should  con- 
tinue to  issue  from  our  candles,  and  when  once  lighted,  and  burn  until  the 
whole  of  the  solid  matter  is  consumed. 

J\frs  B.  The  decomposition  is  commenced  and  continued  by  the  same 
cause.  Such  materials  as  oil  and  tallow,  -when  heated  to  redness,  are  decom- 
posed, and  a  part  of  their  elements  assumes  the  form  of  a  gas,  which  is 
highly  combustible,  and  which  if  ignited  in  presence  of  oxygen  will  conse- 
quently burn(48).  In  order  to  light  a  lamp,  or  candle,  you  apply  sufficient 
heat  to  decompose  some  of  the  oil  or  tallow  contained  in  the  wick.  The  gas 
thus  produced  is  lighted  as  it  escapes,  and  in  burning  continues  to  supply 
sufficient  heat  to  keep  up  the  decomposition(49). 

Caroline.  But  such  is  not  the  case  with  the  gas  lights,  as  the  gas  is  car- 
ried in  pipes  under  ground,  and  kept  ready  to  be  lighted  at  any  time.  How 
is  that  managed? 

Mrs  B.  We  have  repeatedly  burnt  hydrogen  at  the  end  of  a  tube,  as  ra- 
pidly as  it  was  produced;  but  this  same  hydrogen  might  have  been  collected 
in  a  receiver,  and  preserved  for  years.  If  oil,  tallow,  resins,  or  resinous 
•woods  be  put  into  a  retort,  or  flask,  and  heated  to  redness,  the  gas,  instead 
of  being  burnt,  may  be  collected  and  preserved  for  future  use,  and  this  is 
what  is  done  at  the  gas  works(50), 

Emily-  You  told  us,  Mrs  B.,  that  carburetted  hydrogen  was  produced  by 
the  spontaneous  decomposition  of  animal  and  vegetable  matter.  Now  as  this 
is  every  where  going  on,  I  should  have  supposed  that  a  sufficient  quantity  of 
this  gas  would  be  mixed  with  the  atmosphere,  to  take  fire  from  the  burning 
of  our  lamps,  or  from  other  combustions. 

JUrsB.  A  great  number  of  gases  and  vapours  escape  in  the  decay  of 
organized  substances,  which,  were  they  to  continue  to  accumulate,  would 
soon  render  the  globe  uninhabitable;  but  that  kind  Providence  who  has  so 
wisely  regulated  all  these  operations,  disposes  of  them  so  as  to  answer 
many  valuable  ends,  some  of  which  are  within  the  sphere  of  our  observation. 
The  gases  that  are  produced  by  decaying  vegetables  are,  undoubtedly, 
in  many  instances,  decomposed  by  those  that  are  growing,  and  become  part 
of  the  aliment  by  which  they  are  nourished(51). 

I  have  in  this  bottle  a  portion  of  the  carburetted  hydrogen  evolved  from 
vegetable  matter.  I  will  pass  it  up  through  water,  into  a  receiver,  and 
show  you  its  combustion. 

Caroline.  I  should  like  to  know  how  to  collect  it,  but  it  must  require  a 
great  length  of  time,  as  vegetables  decay  very  slowly. 

MrsB.  It  exists  entangled  in  the  mud  at  the  bottom  of  stagnant  waters. 
If  this  be  stirred,  bubbles  of  air  will  rise  to  the  surface,  and  may  be  collected 
by  filling  a  bottle  with  water,  placing  a  funnel  in  its  mouth,  and  inverting  it 
under  the  surface  of  the  pool  or  pond,  so  that  the  funnel  may  conduct  the  bub- 
bles into  the  bottle  as  they  rise,  when  the  mud  below  is  disturbed.  When 
full,  the  tunnel  is  to  be  withdrawn,  and  the  bottle  corked  under  water(52). 


•*7.  What  substances  produce  this  gas  in  abundance? 

48.  By  what  means  may  they  be  made  to  yield  it? 

49.  How  is  it  produced  from  our  lamps  and  candles? 

50.  How  is  it  prepared  and  preserved  for  gas  lights? 

51.  What  is  said  of  its  natural  production  and  decomposition? 

52.  How  may  carburetted  hydrogen  be  collected  from  ponds? 


ON  CARBURETTED  HYDROGEN.          161 


Caroline.  But  how  feebly  it  burns !  If  our  lamps  or  candles  gave  no 
more  light,  they  would  be  but  pQor  substitutes  for  day-light. 

Mrs  JB.  There  are,  at  least,  two  well  defined  species  of  this  gas.  That 
which  you  have  just  seen  is  called  light  carburetted  hydrogen,  and  its  illu- 
minating power  is  very  feeble 5  the  other,  called  heavy  carburetted  hydro- 
gen, burns  with  intense  brilliancy.  In  most  of  the  processes  by  which  we 
obtain  them,  they  are  mixed  together,  and  accordingly  as  one  or  the  other 
predominates,  the  illumination  is  more  or  less  brilliant.  The  heavy  car- 
buretted hydrogen  appears  to  contain  twice  as  much  carbon,  in  proportion 
to  the  hydrogen,  as  exists  in  the  light  kind(53). 

Emily.  What  are  the  two  fluids,  Mrs  B.,  which  you  are  pouring  into  the 
retort?  They  do  not  seem  to  agree  very  well  together. 

Mrs  _ff.  I  am  about  to  collect  some  heavy  carburetted  hydrogen.  The  li- 
quid which  I  first  poured  in  was  alcohol,  or  spirits  of  wine,,  and  I  am  now 
adding,  cautiously,  about  two  or  three  times  its  bulk  of  sulphuric  acid.  The 
mixture  of  these  fluids  sets  free  a  large  portion  of  caloric,  and  if  suddenly 
made  might  break  the  retort. 

Emily.  How  dark  the  mixed  liquid  appears,  although  the  articles  of 
which  it  consists  were  both  colourless(54). 

Mrs  B.  Before  we  have  done  with  them,  they  will  be  much  more  dark;  as 
what  will  remain  of  the  alcohol  will  be  merely  a  black  charcoal. 

Caroline.   Charcoal  in  alcohol !  that  I  never  should  have  guessed. 

Mrs  JB.  Do  you  not  know  that  every  kind  of  spirit  is  distilled  from  vege- 
table materials,  and  must  therefore  be  formed  of  some  of  their  constituents? 
Alcohol,  which  is  merely  pure  ardent  spirit,  consists  of  oxygen,  hydrogen, 
and  carbon;  and  were  the  two  former  materials  removed,  nothing  of  the  al- 
cohol would  remain  but  black  charcoal(55). 


53.  What  different  species  ai*e  there  of  this  gas? 

54.  From  what  materials  may  the  heavy  kind  be  obtained? 

55.  What  is  remarked  respecting  the  constituents  of  alcohol? 

O  2 


I  filled  this  bottle  in  the  manner  I  have  described,  and  will  now  show  you 
the  combustion  of  the  gas. 

Mode  of  collecting  Light  Carburetted  Hydrogen  from  Ponds. 


162  CONVERSATIONS  ON  CHEMISTRY. 

Caroline.  Although  we  have  seen  so  many  examples  of  the  transforming 
effect  of  chemical  combination,  the  interest  and  the  admiration,  if  not  the 
surprise,  which  they  excite  remain  undiminished. 

Alcohol,  it  seems,  consists  of  the  materials  of  which  water  is  formed,  but 
with  the  addition  of  a  quantity  of  charcoal.  I  think  that  I  know  some  per- 
sons who  would  derive  advantage  from  decomposing  the  alcohol  which  they 
use.  They  might  then  safely  quench  their  thirst  with  one  portion  of  it,  and 
warm  themselves  by  means  of  the  other. 

Mrs  B.  Sulphuric  acid  has  a  strong  attraction  for  water,  the  constituents 
of  which  exist  in  the  alcohol.  When  aided  by  a  gentle  heat,  the  attraction  of 
the  acid  promotes  their  union,  and  water  being  thus  formed,  the  alcohol  is 
consequently  decomposed.  It  however  contains  more  hydrogen  than  enters 
into  the  composition  of  the  water,  and  this  excess,  uniting  to  a  part  of  the  car- 
bon, forms  the  heavy  carburetted  hydrogen,  the  gas  which  we  are  now 
collecting.  We  have  thus  disposed  of  the  oxygen,  hydrogen,  and  a 
part  of  the  carbon,  of  which  the  alcohol  consists;  but  a  large  portion  of  the 
carbon  has  nothing  with  which  to  combine,  and  remains  behind  in  the  form 
of  charcoal,  finely  attenuated  and  perfectly  black(56). 

Emily.  But  may  not  the  sulphuric  acid  contribute  some  part  of  its  con- 
stituents to  the  formation  of  the  gas? 

Mrs  B.  That  it  does  not  is  evident  from  the  acid  not  containing  either 
carbon  or  hydrogen;  and  besides  this,  the  chemist  is  able  to  detect  the  whole 
of  the  acid  after  the  process  has  been  completed(57).  I  will  now  burn  the 
gas  by  allowing  }t  to  issue  through  a  tube,  and  then  igniting  it. 

Caroline.  What  a  splendid  light!  Well  may  the  gas  lights  be  more 
brilliant  than  common  lamps,  if  they  contain  any  large  proportion  of  this 
species  of  air(58). 

Mrs  B.  The  name  of  olefiant  gas  was  given  tOfthis  air  by  its  discoverers, 
the  Dutch  chemists:  it  was  so  called  by  them,  because  when  mixed  with  an 
equal  volume  of  another  gas,  called  chlorine,  the  two  condense,  and  form  a 
concrete  substance  resembling  oil.  You  must  recollect  this  name,  as  it  is 
still  frequently  used(59).  All  these  carburetted  gases  are  irrespirable. 

Emily.  As  the  burning  of  carbon  produces  carbonic  acid,  and  the  burn- 
ing of  hydrogen  produces  water,  both  must  result  from  the  combustion  of  this 
gas;  and,  in  fact,  the  tallow  of  our  candles,  and  the  oil  of  our  lamps,  must 
be  converted  into  watery  vapour  and  fixed  air(60). 

Mrs  B.  So  I  was  going  to  inform  you,  but  am  gratified  at  the  frequent 
evidences  of  your  reasoning  upon,  and  deducing  consequences  from,  the 
fa&ts  presented  to  you. 

Do  you  know  what  this  wire  cage  is  which  I  have  upon  the  table? 
Caroline.   I  think  that  I  have  heard  you  call  it  the  safety  lamp.     Is  it 
not  the  contrivance  which  is  said  to  be  so  wonderfully  efficacious  in  prevent- 
ing the  explosions  that  take  place  in  coal  mines?     Have  I  not  also  heard  it 
called  the  Davy  lamp? 

Mrs  B.  It  was  invented  by  Sir  Humphry  Davy,  and  is  universally  ad- 
mitted to  be  the  source  of  one  of  the  most  triumphant  victories  which  science 
has  ever  achieved  by  means  so  simple;  disarming  of  all  its  terrors  a  power 
which  had  frequently,  and  in  a  moment,  spread  death  and  desolation  around, 
and  effecting  this  by  the  aid  of  a  sheet  of  wire  net-work  only(6i). 


56.  By  what  action  of  the  materials  is  the  gas  produced? 
ifrl '.  What  is  observed  respecting  the  sulphuric  acid? 
58.  What  is  noticed  with  regard  to  its  combustion? 
69.   Why  was  this  air  named  olefiant  gas? 

60.  What  is  produced  in  the  burning  of  our  lamps  and  candles? 

61.  What  is  remarked  respecting  the  safety-lamp  ? 


ON  CARBURETTED  HYDROGEN.  163 

In  many  mines  carbonic  acid  is  disengaged  in  large  quantities,  and  when 
the  miners  observe  that  their  lights  burn  dimly,  they  must  retire,  or  be  in 
danger  of  suffocation:  this  gas  is  called  by  them  choke  damp.  In  coal  mines, 
•what  the  miners  call  Jlre  damp,  which  is  light  carburetted  hydrogen,  some- 
times issues  very  abundantly  from  the  fissures  in  the  coal,  and  mixing  with 
the  air  of  the  atmosphere,  forms  an  explosive  compound,  which  takes 
fire  from  the  flame  of  a  lamp,  or  candle,  killing  the  miners,  and  destroying 
their  works(62).  Davy,  however,  ascertained  that  if  the  flame  of  a  lamp 
were  surrounded  completely  by  wire  gauze,  the  meshes  of  which  are  fine,  but 
still  sufficiently  open  to  afford  a  good  light,  it  might  be  safely  carried  into 
the  most  explosive  mixture(63). 

Caroline.  In  looking  at  the  thing,  this  appears  so  unlikely  that  I  cannot 
imagine  by  what  train  of  reasoning  Davy  arrived  at  such  a  conclusion. 

Mrs  B.  He  arrived  at  it  by  the  most  acute  reasoning,  founded  upon 
laborious  experimental  investigation.  Wollaston  had  observed  that  explo- 
sive mixtures  would  not  burn  in  narrow  tubes,  and  Davy,  pursuing  this  idea, 
Found  that  if  the  bore  was  very  small,  the  tube  might  also  be  made  extreme- 
ly short,  and  still  explosive  gases  could  not  be  lighted  through  it.  Now  the 
wire  gauze  may  be  considered  as  formed  of  a  great  number  of  such  tubes, 
the  length  of  which  is  equal  to  the  diameter  of  the  wire(64). 

Emily.  Yet  the  gas  must  pass  freely  through  these  openings,  and  get 
into  the  lamp. 

Mrs  B.  Certainly,  and  sometimes  it  explodes  there  without  doing  any 
harm:  at  others,  the  whole  interior  of  the  lamp  will  be  filled  with  flame,  the 
wire  will  become  red-hot,  and  yet  the  gas  at  the  outside  will  not  be  ignited. 

Caroline.  But  what  can  protect  the  gas  in  the  mine  from  being  ignited 
by  the  red-hotwire  of  the  lamp?  That  seems  incomprehensible. 

•Mrs  B.  It  requires  a  very  intense  heat  to  set  fire  to  the  gas;  and  it  has 
been  ascertained  that  flame,  although  the  light  which  it  emits  may  be  feeble, 
is  much  hotter  than  metal  even  when  at  a  glowing  red  heat.  A  wire  thus 
heated  may  be  safely  put  into  an  explosive  mixture,  whilst  a  shred  of  paper, 
or  a  single  thread,  burning  with  flame,  would  ignite  it(65). 

Caroline.  That  is  so  far  satisfactory,  but  what  can  prevent  the  flame 
itself  from  passing  through  the  meshes? 

Mrs  B.  Flame  can  only  remain  such  at  the  temperature  of  inflamma- 
tion, and  if  you  cool  it  below  this,  it  must  be  extinguished.  Now  the  wire  of 
the  lamp  is  a  good  conductor  of  heat,  and  even  when  red-hot  is  so  much 
cooler  than  the  flame,  that  the  latter  is  extinguished  in  passing  through 
it(66).  This  is  the  theory  of  the  phenomenon  as  given  by  Davy,  and  although 
other  explanations  have  been  offered,  there  would  be  no  advantage  in  our 
discussing  them. 

The  fact  that  flame  will  not  pass  through  a  wire  net  may  be  very  easily 
shown.  Observe,  I  hold  this  piece  of  woven  wire  over  a  jet  of  burning  hy- 
drogen [fig.  1.],  and  the  flame  may,  you  see,  be  flattened  down,  but  will  not 
pass  above  the  meshes,  although  the  gas  passes  freely  through  and  may  be 
lighted  above  them. 

I  will  now  extinguish  the  flame,  and  hold  the  gauze  over  the  tube  as  before, 
allowing  the  gas  to  pass  through  it  [fig.  2.].  You  see  that  I  can  light  the  gas 
above  the  wire,  and  yet  the  flame  will  not  pass  down  to  the  tube  from  which 
it  issues(67). 


62.  What  dangerous  gases  are  produced  in  coal  mines? 

63.  What  fact  did  Davy  discover  respecting  the^re  damp? 

64.  What  observation  of  Wollaston  led  to  this  discovery? 

65.  Why  does  not  the  heated  wire  produce  an  explosion? 

66.  In  what  way  is  the  wire  gauze  believed  to  operate? 

67.  By  what  experiments  is  this  illustrated? 


164 


CONVERSATIONS  ON  CHEMISTRY. 

Safety  Lamp. 


Apparatus  to  show  that  Flame  -will  not  pass 
through  Wire  Gauze. 


Fig.  1.  Fig.  2.  Fig.  3. 

[Fig.  1.  Flame  depressed  by  wire  gauze.  Fig.  2.  Flame  prevented  from 
descending.  Fig.  3.  Davy's  safety  lamp.  A,  Tube  and  wire  whicb  passes 
through  the  bottom  for  trimming  it.  B,  Spout  through  which  oil  is 
supplied.] 

If  you  examine  the  lamp  carefully,  the*use  of  its  different  parts  will  be 
quite  evident.  The  safety  of  the  miner  depends  upon  his  not  opening  it, 
which  he  never  has  occasion  to  do  whilst  he  is  in  the  mine.  There  is  a 
tube  at  the  side  of  the  reservoir  of  oil,  for  the  purpose  of  supplying  it;  and 
in  order  to  raise  or  lower  the  wick,  a  wire  passes  through'  a  tube,  which  it 
fits  exactly,  and  extends  from  the  bottom  to  the  wick(68). 

Emily.  This  is  really  an  interesting  discovery,  and  there  are  but  few 
things  that  you  have  explained  from  which  I  have  derived  equal  pleasure 
and  information. 

Mrs  B.  There  are  some  compounds  of  carbon  and  hydrogen  that 
exist  in  the  liquid  form.  When  I  exhibited  -potassium  to  you,  I  informed 
you  that  the  liquid  in  which  it  was  kept  was  called  naphtha,  and  that  it  did 
not  contain  any  oxygen.  It  is,  in  fact,  a  liquid  compounded  of  carbon  and 
hydrogen  only,  and  is  therefore  a  carburet  of  hydrogen. 

Emily.     Is  this  a  natural  production,  or  is  it  formed  by  art? 

MrsJB.  Naphtha  is  a  mineral  fluid  which  exudes  from  the  earth  in 
some  parts  of  the  United  States,  in  Italy,  and  on  the  banks  of  the  Caspian. 
A  large  quantity  is,  however,  now  obtained  by  distilling  coal  tar,  which  is 
produced  at  the  establishments  where  gas  is  made  from  pit  coal.  It  is  pro- 
bable that  the  natural  and  artificial  productions  are  exactly  alike  in  their 
composition:  at  all  events  they  preserve  potassium  equally  well,  have  the 
same  odour,  and  burn  with  a  like  brilliant  flame.  Naphtha  is  nearly  as 
light  as  ether,  which  is  the  lightest  liquid  known(69). 

There  is  a  curious  compound  of  sulphur  and  carbon,  which  may  receive 
a  passing  notice  with  the  other  carburets.  Carbon  and  sulphur  may  be 
made  to  combine,  and  to  exist  in  the  form  of  a  transparent  and  colourless 
liquid.  This  sulphuret,  or  rather  bisulphuret  of  carbon  is  very  inflammable, 


68.  How  is  the  safety  lamp  constructed  ? 

69.  What  are  the  constituents  and  properties  of  naphtha? 


ON  THE  ALKALIES.  165 

acrid  to  the  taste,  and  has  a  very  offensive  odour.  It  may  be  formed  by 
passing  the  vapour  of  sulphur  over  fragments  of  red-hot  charcoal.  The  fact 
of  the  existence  of  such  a  combination  is  all  that  would  at  present  interest 
you  in  regard  to  it(70). 

Our  subject  has  detained  us  rather  longer  than  usual,  but  you" appear  to 
have  been  too  much  interested  to  think  of  fatigue.  There  are  some  other 
carburets  which  we  shall  examine,  but  not  at  present.  I  think  it  necessary, 
instead  of  proceeding  in  a  course  which  might  be  accounted  more  systematic, 
to  give  you  some  further  information  respecting  the  alkalies,  and  to  examine 
the  earths  and  metals,  after  which  I  shall  explain  to  you  the  laws  of  chemi- 
cal combination.  These  subjects  will,  I  apprehend,  fully  occupy  us  for 
three  or  four  meetings.  I  thought  that  you  would  be  gratified  by  a  know- 
ledge of  the  course  I  intend  to  pursue,  as  it  may  guide  you  in  your  prepa- 
ratory reading. 


CONVERSATION  XVI. 

ON  THE  ALKALIES. 

Distinguishing  Characters  of  the  Alkalies.  Fixed  and  Volatile  Alkalies. 
Potassa.  Soda.  Formation  of  Soap.  Caustic  and  Mild  Jllkalies.  Am- 
monia. Sal  Ammoniac.  Liquid  Ammonia.  Formation  of  Ammonia  by  the 
decomposition  of  Animal  Matter.  Carbonate  of  Ammonia. 

Mrs  B.  It  is  no  easy  matter  to  make  much  progress  in  chemistry  with- 
out acquiring  some  considerable  knowledge  of  the  alkalies;  as,  in  consequence 
of  their  numerous  combinations,  we  meet  with  them  at  almost  every  step  of 
our  journey.  I  have  therefore  thought  it  necessary  on  some  previous  occa- 
sions to  call  your  attention  to  them,  and,  before  we  proceed  further,  shall 
give  you  such  other  particulars  respecting  them  as  may  appear  to  me  of  the 
most  importance;  and  should  some  of  the  facts  which  have  been  already 
noticed  be  repeated,  I  am  not  apprehensive  thatyou  will  complain  of  their 
being  made  too  familiar  to  you. 

Emily.  No,  indeed,  Madam;  we  feel  very  sensibly  that  most  of  them 
will  not  only  bear,  but,  for  our  sakes,  will  need  repetition;  and  for  my  own 
part,  I  am  convinced  that  I  should  find  more  to  glean  in  passing  a  second 
time  over  the  same  ground,  than  I  shall  have  gathered  in  the  first  instance. 

Mrs  B.  THE  ALKALIES  are  characterized  by  a  peculiar  acrid  taste,  by 
their  action  upon  coloured  vegetable  infusions,  turning  the  blue  tinctures 
green,  and  by  their  neutralizing  the  properties  of  the  acids;  with  the  whole 
of  which  they  combine  and  form  salts(l).  Some  of  the  earths  so  nearly 
resemble  the  alkalies  in  their  properties,  as  to  have  acquired  the  name  of 
alkaline  earths:  in  fact,  it  is  not  now  uncommon,  in  systems  of  chemistry,  to 
omit  placing  the  alkalies  in  a  class  by  themselves(2).  I  am  convinced, 
however,  that,  both  in  this  and  other  instances,  a  departure  from  strict  syste- 
matic rules  will  facilitate  your  course. 

Formerly  the  alkalies  were  said  to  be  three  in  number,  POTASSA,  SODA, 
and  AMMONIA;  the  name  of  fixed  alkalies  being  given  to  the  two  former, 
because  they  are  not  easily  volatilized,  whilst  ammonia  was  denominated 
the  volatile  alkali^  because,  in  its  uncombined  state,  it  exists  as  a  gas. 


70.   What  combination  does  carbon  form  with  sulphur? 

1.  By  what  properties  are  the  alkalies  characterized? 

2.  What  is  observed  respecting  some  of  the  earths  > 


166  CONVERSATIONS  ON  CHEMISTRY. 


A  third  fixed  alkali  was  discovered  a  few  years  ago;  but  as  it  has  been  found 
in  very  small  quantities  only,  the  mere  facts  of  its  having  been  named 
LITHIA,  and  of  its  agreement  with  the  other  fixed  alkalies  in  being  a  com- 
pound of  oxygen  with  a  metallic  base,  comprise  all  that  I  shall  say  to  you 
about  it(3). 

Within  a  few  years  chemists  have  also  ascertained  that  the  active  properties 
of  many  vegetable  products  are  in  their  nature  alkaline.  The  consideration 
of  these  substances,  however,  will  belong  to  vegetable  chemistry,  as  they 
are  the  result  of  vegetable  organization,  and  contain  the  ordinary  principles 
of  vegetable  matter(4). 

I  think,  young  ladies,  that  you  have  a  distinct  recollection  of  the  composi- 
tion of  potassa  and  soda. 

Caroline.  We  recollect  it  perfectly,  and  have  frequently  conversed  to- 
gether upon  the  experiment  of  the  burning  of  potassium  upon  water;  its 
decomposing  that  fluid  to  unite  with  its  oxygen,  and  thus  being  convert- 
ed iato  potash.  The  nature  of  the  metallic  bases  of  potash  and  of  soda  is 
too  intimately  associated  with  the  recollection  of  this  experiment  for  us  ever 
to  forget  it(5). 

Mrs  B.  The  white  substance  which  you  see  in  this  phial  is  pure  POTAS- 
SA. It  is  very  difficult  to  preserve  it  in  the  solid  state,  as  it  is  extremely 
deliquescent,  that  is,  attracts  the  moisture  from  the  atmosphere  with 
great  avidity;  and  if  the  air  were  not  perfectly  excluded,  it  would,  in  a  very 
short  time,  be  actually  dissolved(G). 

Emily.     I  suppose  then  that  it  is  always  found  in  a  liquid  state. 

Mrs  B.  No:  it  is  never  found  in  nature  in  a  pure  uncombined  state,  but 
exists  in  a  variety  of  forms  and  combinations.  That  which  we  procure  from 
the  shops  under  the  name  of  potash,  contains  carbonic  acid,  and  is,  chemi- 
cally speaking,  a  carbonate  of  potash,  or  of  potassa(T). 

Potash  was  formerly  called  the  vegetable  alkali,  because  that  which  is 
used  in  the  arts  is  procured  from  the  ashes  of  vegetables,  and  principally 
from  wood  ashes.  In  like  manner  soda  was  called  the  mineral  alkali.  These 
names,  however,  are  not  merely  unnecessary,  but  improper,  as  each  of  these 
alkalies  is  found  both  in  the  vegetable  and  mineral  kingdoms(8). 

Caroline.  I  observe  that  you  use  the  terms  potash  and  potassa  to  desig- 
nate the  same  substance:  ought  we  not  to  restrict  ourselves  to  one  of  them? 

JWrs  B.  They  are  frequently  used  indiscriminately,  as  perfect  synonymes; 
but  by  potash  is  generally  intended  the  impure  alkali  as  we  find  it  in  com- 
merce, and  by  potassa,  the  pure  substance,  separated  from  all  foreign  mat- 
ter. We  shall  not,  however,  strictly  confine  ourselves  to  these  distinc- 
tions^). 

Emily.  As  potash  is  contained  in  vegetables,  and  is  so  very  soluble,  I 
suppose  it  can  be  separated  by  soaking  them  in  water. 

J\frs  B.  We  are  not  very  well  informed  of  the  state  in  which  potash 
exists  in  most  vegetables;  for  although  some  of  its  salts  can  be  obtained  from 
the  juices  of  certain  plants,  it  is  usually  so  intimately  combined  with  the  other 
vegetable  constituents,  as  not  to  be  capable  of  separation  until  they  are  decom- 
posed by  burning,  when  its  fixed  nature  causes  it  to  remain  behind  after  all 
the  volatile  ingredients  are  teparated.  The  alkali  has  a  strong  affinity  for  car- 
bonic acid,  and  therefore  combines  with  a  portion  of  that  which  is  produced 


3.  Name  the  alkalies,  and  the  manner  of  designating  them. 

4.  What  other  alkaline  substances  have  been  discovered? 

5.  Of  what  are  potassa  and  soda  composed? 

6.  What  effect  has  the  atmosphere  on  potassa? 

7.  What  is  the  nature  of  the  potash  of  commerce  ? 

8.  How  were  potash  and  soda  formerly  distinguished? 

9  What  is  observed  respecting  the  terms  potash  and  potassa? 


ON  THE  ALKALIES.  167 

by  the  combustion  of  the  carbon  of  the  wood,  and  hence  it  is  always  first 
obtained  in  the  form  of  a  carbonate(lO). 

Caroline.     Of  what  ingredients  do  the  ashes  of  burnt  vegetables  consist? 

Mrs  B.  The  insoluble  parts  principally  consist  of  some  of  the  earths  and 
metallic  oxides;  and  the  soluble  ingredients  are  the  carbonate  of  potash,  and 
small  portions  of  some  other  saline  substances(ll).  By  pouring  water  upon 
the  ashes,  the  salts  are  dissolved,  whilst  the  insoluble  portion  of  the  ashes 
remains  at  the  bottom  of  the  vessel.  The  solution  is  then  put  into  iron 
pots,  and  the  water  boiled  away.  When  the  evaporation  is  completed,  the 
carbonate  of  potash,  mixed  with  the  other  salts,  is  obtained  in  a  dry  state,  and 
forms  the  potash  of  the  shops,  which  undoubtedly  derived  its  name  from  the 
pots  in  which  it  is  prepared(12). 

Pearlash  is  the  same  substance,  partially  purified.  It  is  also  sold  under 
the  names  of  salt  of  tartar  and  salt  of  ivormivood;  but  in  this  case  it  is 
usually  still  further  purified  from  the  foreign  salts(13). 

Emily,  Still,  neither  of  these  is  potassa:  they  are  carbonates,  and 
of  course  we  cannot  examine  the  properties  of  the  pure  article  when  com- 
bined with  an  acid.  In  what  way  can  it  be  deprived  of  its  carbonic  acid? 

Mrs  B.  Lime  has  a  strong  affinity  for  carbonic  acid,  and  will  separate 
it  from  potash.  For  this  purpose  we  take  quicklime,  that  is,  lime  which 
has  been  deprived  of  its  carbonic  acid.  This  we  mix  with  a  solution  of  potash, 
and  heat  the  mixture;  a  carbonate  of  lime  will  then  be  formed  and  precipi- 
tated, whilst  the  caustic  potash  will  remain  in  the  liquid,  and  may  be  ob- 
tained in  the  solid  state  by  evaporation(l4). 

Caroline.  Now  I  understand  the  use  of  lime  when  soft  soap  is  made,  and 
perceive  how  it  sharpens  the  ley,  as  the  servants  say.  The  water  which  soaks 
through  the  wood  ashes,  and  forms  the  ley,  becomes  charged  with  potash, 
or  rather  is  a  solution  of  the  carbonate  of  potash;  and  the  addition  of  quick- 
lime removes  the  carbonic  acid,  renders  the  ley  caustic,  and  accelerates  the 
formation  of  the  soap(15). 

Mrs  B.  You  will  soon,  I  hope,  make  a  good  housewife,  and  be  able 
to  superintend  the  process  which  you  have  so  well  described.  Potash  and 
soda  both  form  soap  when  combined  with  fat,  or  oils;  the  former  producing 
soft,  and  the  latter  hard  soap.  To  cause  them  to  combine  with  the  fatty 
matter,  it  is  proper  to  render  them  caustic;  as  their  combination  with  an 
acid  would  interfere  with  their  tendency  to  unite  with  any  other  article(16). 
Some  curious  information  with  respect  to  the  chemical  composition  of  soap 
I  must  reserve  until  we  have  examined  the  nature  of  animal  and  vegetable 
oils. 

Caroline.  By  the  mild  alkali  which  you  mentioned,  it  appears  that  the 
carbonate  is  intended,  and  by  the  caustic,  the  alkali  deprived  of  its  carbonic 
acid  ? 

Mrs  B.  Yes,  but  these  are  considered  as  old  names.  They  are,  however, 
so  expressive  of  the  difference  in  the  two  states  of  the  alkali,  that  they  are 
not  unfrequently  used,  and  are  not  likely  to  be  entirely  dismissed.  The 
caustic  alkali  rapidly  corrodes  the  skin  and  the  flesh,  converting  them  into 


10.  What  is  said  of  the  combination  of  potash  with  the  other  vegetable 
constituents,  and  of  its  conversion  into  a  carbonate? 

11.  What  articles  are  contained  in  the  ashes  of  vegetables? 

12.  How  is  the  potash  separated,  and  why  is  it  so  named? 

13.  By  what  other  names  is  it  known? 

14.  How  may  it  be  separated  from  the  carbonic  acid? 

15.  What  does  Caroline  remark  concerning  the  making  of  soap? 

16.  What  constitutes  the  difference  between  hard  and  soft  soap? 


168  CONVERSATIONS  ON  CHEMISTRY. 

- 

a  soapy  substance.     When  mixed  with  lime,   it  is  used  by  surgeons  as  a 
caustic,  under  the  name  of  lapis  infernalis(l7). 

With  potassa  we  have  yet  much  to  do,  as  it  not  only  combines  with  all 
the  acids,  forming  a  very  great  number  of  different  salts,  but  it  is  also  an 
ingredient  in  many  other  natural  and  artificial  compounds,  and  particularly 
in  that  beautiful  material,  glass,  Avhich  is  produced  by  simply  fusing  com- 
mon sand  with  potash,  or  with  soda(l8). 

Emily.  What  an  extremely  useful  substance  is  potash!  I  feel  curious  to 
hear  something  more  respecting  the  employment  of  it  in  making  glass. 

Mrs  B.  You  will  soon  be  gratified  in  this  particular,  but  not  until  after 
we  have  examined  the  earths  that  are  concerned  in  making  it. 

We  must  now  proceed  to  SODA,  which,  however  important,  will  detain  us 
but  a  very  short  time,  as,  in  all  its  general  properties,  it  very  strongly  re- 
sembles potash.  Indeed,  so  great  is  their  similitude,  that  they  were  long 
confounded,  and  they  can  now  scarcely  be  distinguished,  except  by  the  dif- 
ference of  the  salts  which  they  form  with  acids. 

The  great  source  of  this  alkali  is  the  sea,  where,  combined  with  a  pecu- 
liar acid,  it  forms  the  salt  with  which  the  waters  of  the  ocean  are  so  strong- 
ly impregnated. 

Emily.     Is  not  that  the  common  table  salt? 

Mrs  B.  The  very  same;  but  we  must  postpone™  entering  into  the  par- 
ticulars of  this  interesting  combination,  as  you  are  not  yet  acquainted  with 
its  ^constituents.  Soda  may  be  obtained  from  common  salt;  but  the 
usual  method  of  procuring  it  is  by  the  combustion  of  marine  plants,  an 
operation  perfectly  analogous  to  that  by  which  potash  is  obtained  from  land 
vegetables(lO). 

Emily.      From  what  does  soda  derive  its  name  ? 

Mrs  B.  From  a  plant  called  by  us  soda,  and  by  the  Arabs  kali,  which 
affords  it  in  great  abundance.  Kali  has,  indeed,  given  its  name  to  the  al- 
kalies in  general. 

Caroline.  If  potassa  and  soda  resemble  each  other  so  nearly^  may  they 
not  be  really,  as  was  formerly  supposed,  the  same  substance,  only  modified 
by  some  particular  circumstances  not  well  understood? 

Mrs  B.  Neither  you  nor  I  are  justified  in  making  such  a  conjecture. 
The  able  chemists  who  have  devoted  their  lives,  not  to  guessing,  but  to  ex- 
periments of  research  in  their  laboratories,  must  not  only  be  allowed,  but 
have  a  right  to  decide  questions  of  this  sort  for  those  who  are  only  chemists 
of  the  parlour.  Have  you  forgotten  the  fact  of  the  decomposition  of 
these  alkalies,  and  the  difference  in  the  properties  of  potassium  andsodium? 
If  these  are  different,  as  they  are  the  bases  of  the  substances  in  question,  all 
their  combinations  must  necessarily  be  so  likewise.  The  saline  bodies, 
formed  by  the  combinations  of  each  of  these  alkalies  with  the  same  acid,  you 
will,  in  general,  find  to  be  very  plainly  marked  with  distinctive  charac- 
ters^). 

<     Caroline.     I  confess,  madam,  that  your  mild  rebuke  was  well  merited:  < 
So  young  a  chemist  as  I  am,  or  rather  a  mere  novice  in  the  science  like  myself, 
may  well  be  satisfied  to  listen  and  inquire,  without  offering  her  own  crude 
conjectures. 

Mrs  B.  AMMONIA,  or  the  VOLATILE  ALKALI,  must  now  receive  some  at- 
tention. ' 

— 

17.  What  is  said  concerning  the  caustic  and  the  mild  alkalies? 

18.  What  combinations  are  formed  with  the  fixed  alkalies? 

19.  Whence  is  soda  principally  obtained,  and  what  is  said  respecting  it? 

20.  By  what  is  the  difference  between  potash  and  soda  proved? 


ON  THE  ALKALIES. 


169 


Emily.  I  long  to  hear  something  of  this  alkali;  is  it  not  of  the  same 
nature  as  hartshorn? 

Mrs  JB.  Yes,  it  is,  as  you  -will  see  by-and-by.  This  alkali,  being  a 
gas,  is  not  found  in  nature  in  its  pure  state.  It  was  formerly  extracted,  ex- 
clusively, from  a  salt,  called  sal  ammoniac,  which  was  imported  from  Am- 
monia, a  region  of  Lybia,  from  which  country  the  salt  and  the  alkali  both 
derive  their  names.  Some  of  the  salt  is  contained  in  this  bottle;  it  con- 
sists of  a  combination  of  ammonia  and  muriatic  acid(21). 

Caroline.  Then  it  should  be  called  muriate  of  ammonia ;  for  though  I 
am  ignorant  what  muriatic  acid  is,  yet  I  know  that  its  combination  with 
ammonia  cannot  but  be  so  called,  and  I  am  surprised  to  see  sal  ammoniac 
inscribed  on  the  label. 

Mrs  JB.  That  is  the  name  by  which  it  has  been  so  long  known,  that  the 
modern  chemists  have  not  yet  succeeded  in  banishing  it  altogether.  It 
is  still  so  denominated  by  druggists,  though  by  scientific  chemists  it  is  more 
properly  called  muriate  of  ammonia. 

Emily.  And  how  is  the  alkali  separated  from  this  salt,  so  as  to  obtain  it 
in  the  gaseous  state? 

Mrs  J3.  By  the  same  substance  which  separates  carbonic  acid  from  the 
carbonate  of  potassa. 

If  equal  parts  of  dry,  slaked,  quicklime  and  muriate  of  ammonia  be 
mixed  together,  and  put  into  a  retort,  on  applying  heat  the  gaseous  or  vol- 
atile ammonia  will  be  expelled. 

Emily.  Then,  as  the  carbonic  acid  united  with  the  lime  in  the  case  of 
potassa,  so,  in  the  present  instance,  what  you  call  muriatic  acid  must  do  the 
same,  and  a  muriate  of  lime  be  formed(22). 

Mrs  JB.     Your  conjecture,   or  rather  your  judgment,  is  correct  in  this 
particular;  and  I  am  happy  to  find  you  so  well  pre- 
pared to  trace  some  of  those  more  complex  operations 
of  chemistry   to  which   your  attention  will  soon  be 
called. 

Emily.  Cannot  we  collect  some  of  this  gaseous  am- 
monia by  means  of  the  pneumatic  cistern? 

Mrs  B.  That  would  be  impossible,  unless  we  were 
to  keep  the  water  highly  heated,  as  water  at  common 
temperatures  absorbs  this  gas  very  rapidly.  If  kept 
cold  by  ice,  it  will  condense  about  700  times  its  own 
bulk.  Water,  when  impregnated  with  this  gas,  is  call- 
ed liquid  ammonia,  aqua  ammonias,  or  spirits  of  harts- 
horn(23). 

For  collecting  the  gases  which  are  readily  absorbed 
by  water,  the  chemist  uses  a  cistern  and  receivers,  filled 
•with  mercury;  but  although  I  am  not  provided  with 
this  apparatus,  we  can  contrive  to  collect  some  of 
the  gas,  as  we  formerly  collected  hydrogen,  in  con- 
sequence of  the  difference  between  its  specific  gravity 
and  that  of  atmospheric  air.  The  principle  upon  which 
this  operation  depends  you  very  well  understand(24). 
Caroline.  From  the  manner  in  which  you  have 
fixed  the  apparatus,  this  gas,  like  hydrogen,  must  be 
lighter  than  the  air  of  the  atmosphere.  The  materials 


Gaseous  Ammonia 
collected  in  an  open 
Flask. 


21.  What  is  ammonia,  and  why  was  it  so  named? 

22.  How  is  it  separated  from  muriate  of  ammonia? 
25.  What  is  remarked  of  its  absorption  by  water? 
24.  In  what  way  is  this  gas  usually  collected? 


170  CONVERSATIONS  ON  CHEMISTRY. 

•which  produce  it  are  contained  in  the  lower  vessel.  From  these,  the  heat  will 
disengage  it,  and  its  levity  will  cause  it  to  ascend  through  the  tube  into  the 
flask  above,  where  gradually  accumulating,  it  will  force  out  the  common 
air  and  occupy  its  place(25). 

Emily.  I  already  smell  its  pungent  odour,  just  like  that  of  hartshorn,  or 
of  the  volatile  smelling  salts,  which,  when  not  too  strong,  I  think  very 
agreeable. 

Mrs  B.  If  we  now  remove  the  flask  carefully,  and  immerse  its  mouth 
in  water,  the  liquid  will  rapidly  ascend,  and,  were  no  common  air  mixed 
with  the  ammonia,  the  water  would  completely  fill  the  glass. 

Emily.  Certainly;  because  the  water  will  absorb  the  gas,  and  the  pres- 
sure of  the  atmosphere  will  force  it  up  to  fill  the  vacuum  which  would 
otherwise  be  formed  by  this  absorption(26). 

Pray  is  ammonia  similar  in  its  composition  to  the  fixed  alkalies? 

Mrs  B.  Gaseous  ammonia  was  first  obtained  by  Dr  Priestley,  but  its 
composition  was  ascertained  by  the  celebrated  French  chemist  Berthollet, 
who  discovered  that  it  consists  of  about  one  part  of  nitrogen  combined 
with  three  parts  of  hydrogen.  He  decomposed  it  by  confining  a  portion  of 
the  gas  over  mercury,  and  causing  a  succession  of  electrical  sparks  to  pass 
through  it:  he  found  that  when  thus  treated,  it  increased  in  bulk,  lost  all  its 
odour  and  its  alkaline  properties,  and  was  actually  converted  into  a  mere 
mixture  of  nitrogen  and  hydrogen  gases.  The  latest  and  most  accurate  ex- 
periments have  confirmed  this  fact,  and  prove  that  when  these  gases  com- 
bine to  form  ammonia,  they  are  condensed  into  one-half  their  previous 
volume;  that  is,  could  we  cause  one  pint  of  nitrogen  to  combine  with  three 
of  hydrogen,  they  would  produce  but  two  pints  of  ammonia.  They  do  not 
unite,  however,  unless  one  or  both  of  the  gases  is  in  a  nascent  state(27). 

Caroline.  Has  the  chemist  discovered  the  mode  of  manufacturing  am- 
monia by  causing  its  constituents  to  combine?  I  conclude  that  this  is  the 
case,  from  your  mentioning  whence  it  was  formerly  procured. 

Mrs  B.  Nearly  the  whole  of  what  is  now  used  in  chemistry  and  the  arts 
is  produced  by  the  combination  of  its  elements.  When  animal  substances  are 
decomposed,  either  spontaneously  or  by  art,  among  the  numerous  products 
which  are  formed,  ammoniacal  gas  results  from  the  combination  of  portions 
of  their  nitrogen  and  hydrogen  with  each  other. 

Bones,  or  other  solid  animal  matter,  are  put  into  large  iron  retorts.  These 
are  heated  to  redness,  and  the  volatile  products  conducted  through  tubes 
into  water,  where  those  of  them  which  are  susceptible  of  it  are  condensed. 
Among  these  is  ammonia  in  a  very  impure-state,  and  combined  with  the  acid 
products  of  the  decomposition,  but  capable,  by  proper  agents,  of  being  sepa- 
rated from  them  and  applied  to  use(28). 

Emily.     Is  the  volatile  alkali  equally  caustic  with  the  fixed? 

Mrs  B.  Potash  and  soda  themselves  are  not  alike  in  this  respect,  the 
former  being  the  most  caustic;  but  it  is  difficult  to  compare  them  with  am- 
monia, which  is  a  gas.  This  gaseous  alkali,  however,  irritates  the  skin  very 
much,  especially  when  it  touches  the  eyes,  or  passes  into  the  nostrils  undi- 
luted; and  there  appears  reason  to  believe  that  if  it  existed  in  a  solid  state, 
its  caustic  action  would  be,  at  least,  as  powerful  as  that  of  potash(29). 

You  have  seen  one  salt,  muriate  of  ammonia,  in  which  this  alkali  and  the 
acid  exist  in  the  solid  form,  and  yet  both  of  its  constituents  are  gaseous. 


25.  How  may  it  be  obtained  without  a  mercurial  trough? 

26.  What  experiment  is  mentioned  showing  its  absorption  by  water? 

27.  What  is  its  composition,  and  how  was  this  ascertained? 

28.  By  what  process  is  ammonia  now  manufactured? 

29.  What  is  said  respecting  the  causticity  of  ammonia? 


ON  THE  ALKALIES.  171 

The  same  is  the  case  with  the  carbonate  of  ammonia,  or  volatile  smelling 
salts,  an  article  with  which  you  are  familiar.  Whenever  the  two  gases, 
carbonic  acid  and  ammonia,  come  into  contact  with  each  other,  they  com- 
bine and  become  solid(SO). 

The  tubes  from  these  two  flasks  pass  into  the  same  receiver.  From  one 
of  them  issues  carbonic  acid,  from  the  other  ammonia;  and  the  white  cloud 
which  fills  the  receiver  is  the  salt  in  question.  This  cloud  will  soon  condense 
and  form  an  incrustation  upon  the  inside  of  the  glass(31). 


Formation  of  Carbonate  of  Ammonia. 


[A.  Flask  containing  quicklime  and  sal  ammoniac.  B.  Flask  with  carbo- 
nate of  lime  and  sulphuric  acid.  C.  The  globe  into  which  the  two  gases 
are  conducted  and  in  which  they  combine  together.  ] 

Caroline.  This  last  experiment  is  equally  pleasing  and  satisfactory,  as  it 
affords  an  interesting  example  of  the  change  of  form  produced  by  chemical 
combination,  and  gives  us  some  new  information  respecting  an  old  acquaint- 
ance. 

J\frs  B.  A  short  summary  of  the  properties  of  ammonia  is  all  that  time 
will  allow  me  to  add,  after  which  we  must  dismiss  it  with  the  certainty  of 
meeting  it  again  in  other  company. 

Ammonia  is  irrespirable;  an  animal  immersed  in  it  being  immediately 
killed.  It  extinguishes  burning  bodies,  neither  of  its  constituents  being 
supporters  of  combustion.  It  is  itself  combustible,  as  it  will  burn,  although 
but  feebly,  when  ignited  in  contact  with  atmospheric  air;  its  hydrogen 
uniting  to  the  oxygen  of  the  atmosphere  and  forming  water,  leaving  its 
nitrogen  free.  Combining  with  the  acids,  it  becomes  the  base  of  a  large 
number  of  salts.  By  powerful  pressure,  assisted  by  cold,  it  can  be  coiv 
densed  into  the  liquid  form(32). 

To-morrow  we  will  occupy  ourselves  with  an  inquiry  into  the  nature  of 
the  earths,  several  of  which,  in  their  properties,  are  nearly  allied  to  the 
fixed  alkalies,  and  in  their  composition  are  known  to  be  analogous  to  potassa, 
soda,  and  lithia. 


SO.  What  is  said  of  the  combination  of  ammonia  and  carbonic  acid? 

31.  By  what  means  may  the  carbonate  of  ammonia  be  collected? 

32.  Give  a  summary  of  the  properties  of  ammonia.        ?    _ 


172  CONVERSATIONS  ON  CHEMISTRY. 


CONVERSATION  XVII. 

ON    THE    EARTHS    AND    SOME    OF   THEIR   COMBINATIONS, 
AND  ON  METEORIC  STONES. 

Alkaline  Earths.  Lime.  Quicklime.  Slaked  Lime.  Lime-water. 
Carbonate  and  Sulphate  of  Lime.  Lime  as  a  Manure.  Calcium.  Bary- 
ta, or  Barytes.  Strontia.  Barium  and  Strontium.  Magnesia.  Car- 
bonate and  Sulphate  of  Magnesia.  Magnesium.  Silex.  Glass.  Vitri- 
fication of  Earths.  Enamels.  Silicon.  Alumina,  or  Argil.  Pottery. 
Earthenioare  and  Porcelain.  Aluminum.  Zirconia.  Glucina,  Yttria  and 
Thorina.  Meteoric  Stones. 

Mrs  B.  THE  EARTHS  are  ten  in  number.  By  some  chemists  three, 
but  more  frequently  four  of  them,  are  called  alkaline  earths,  because  they 
possess  so  many  properties  in  common  with  the  fixed  alkalies.  The  four 
to  which  I  allude  are  lime,  baryta  or  barytes,  strontia  or  strontites,  and 
magnesia.  The  other  five  are  named  silica  or  silex,  alumina  or  alumine, 
zirconia  or  zircon,  glucina  or  glucine,  and  yttrta(\.). 

Emily.  What  we  usually  term  earth,  consists  of  matter,  which  when 
dry  is  in  fine  powder;  but  I  understand  that,  chemically  speaking,  the  state 
of  aggregation  is  disregarded,  and  that  rocks  and  stones  are  considered  as 
earths,  just  as  much  as  sand  and  clay. 

Mrs  B.  To  attempt  to  define  what  is  meant  by  the  earths  is  unnecessary, 
and  would  rather  embarrass  than  aid  us;  as  the  different  properties  by  which 
they  are  distinguished  are  not  possessed  in  the  same  degree  by  the  whole 
class. 

The  substances  which  we  term  earths,  constitute  the  greatest  part  of  the  so- 
lid crust  of  the  globe,  and  they  are  of  peculiar  interest,  not  only  from  their 
abundance,  but  from  their  extensive  use  in  the  arts.  Of  the  ten  which  I 
have  named,  three,  glucina,  zirconia,  and  yttria,  are  very  rarely  found,  and 
two  others,  baryta  and  strontia,  are  scarcely  employed  excepting  as  ehe- 
mical  agents;  so  that,  as  regards  the  arts,  four  only  are  of  much  interest, 
namely,  lime,  magnesia,  silica,  and  alumina(£), 

Rocks  and  stones  generally  consist  of  two  or  more  of  these  earths,  and 
often  contain  some  metallic  matter.  When  we  obtain  the  earths  in  a  state 
of  the  greatest  purity,  they  are  in  the  form  of  a  dry  white  powder,  without 
smell,  and,  most  of  them,  without  taste.  Some  are  sparingly  soluble,  and 
Others  insoluble  in  water.  They  are  all  incombustible,  being,  like  the 
alkalies,  products  of  combustion.  Most  of  them  are  known  to  be  formed  of 
metallic  bases  combined  with  oxygen(3). 

Caroline.  The  soil  of  our  fields  and  gardens  appears  then  to  consist  of 
some  of  these  earths  in  powder,  mixed  with  decayed  animal  and  vegeta- 
ble matter,  to  which,  of  course,  it  owes  its  fertility. 

Mrs  B.  The  earths  form  the  solid  basis  of  the  soil,  and  enter,  though 
sparingly,  into  the  composition  of  the  animals  and  vegetables  which  exist 
on  its  surface.  The  latter  of  these,  however,  as  you  justly  observe,  derive 


1.  Name  the  earths,  distinguishing  those  called  alkaline. 

2.  What  general  remarks  are  made  concerning  them? 

3.  What  is  the  constitution  of  the  earths,  and  what  is  said  of  rocks  and 
stones? 


ON  THE  EAUTHS.  173 

their  principal  nutriment  from  the  same  materials  which  had  previously  en- 
tered into  the  constitution  of  .organized  beings(4). 

Placing  the  alkaline  earths  the  first  upon  the  list,  we  will  now  inquire 
into  the  properties  of  lime. 

LIME  is  strongly  alkaline.  In  nature  it  is  not  met  with  in  its  sim- 
ple state,  but  united  either  with  other  earths,  or  with  acids.  Its  affinity 
for  water  and  carbonic  acid  is  so  great,  that  it  is  -most  commonly  found 
combined  with  these  substances,  with  which  it  forms  the  common  lime- 
stone; but  whenever  a  sufficient  degree  of  heat  is  applied,  it  is  separated 
from  these  ingredients,  which  are  volatilized.  What  is  called  burning  of 
lime,  is  merely  heating  it  red-hot  in  a  kiln,  in  order  to  drive  off  these  in- 
gredients, which  amount  to  half  the  original  weight  of  the  stone(5). 

Emily.  Quicklime,  then,  is  nothing  but  lime-stone,  which  has  been  de- 
prived, in  the  kiln,  of  its  water  and  carbonic  acid  ? 

Mrs  B.  Precisely.  Quicklime  is  so  caustic,  that  it  is  capable  of  decom- 
posing the  dead  bodies  of  animals  very  rapidly,  without  their  undergoing  the 
process  of  putrefaction.  I  have  here  a  lump  of  quicklime  recently  prepared, 
for  had  it  been  long  exposed  to  the  atmosphere,  it  would  have  absorbed 
moisture  from  it,  and  have  become  slaked.  Here  is  also  some  common 
unburnt  lime-stone — we  will  pour  a  little  water  on  each,  and  observe  the 
effects  which  result  from  it. 

Caroline.  How  the  quicklime  hisses!  It  has  become  excessively  hot! — 
It  swells,  and  now  it  bursts  and  crumbles  into  powder,  while  the  water  ap- 
pears to  produce  no  kind  of  alteration  on  the  lime-stone(G). 

Mrs  B.  Because  the  lime-stone  is  already  saturated  with  water,  whilst 
the  quicklime,  which  has  been  deprived  of  it  in  the  kiln,  combines  with  it 
with  very  great  avidity,  and  produces  that  great  disengagement  of  heat,  the 
cause  of  which  I  formerly  explained  to  you:  do  you  recollect  it? 

Emily.  Yes;you  said  that  the  heat  did  not  proceed  from  thelime,  but  from 
the  water,  which  was  solidified,  and  consequently  parted  with  its  latent  heat. 

Mrs  B.  Very  well.  If  we  continue  to  add  successive  quantities  of  wa- 
ter to  the  lime,  after  being  slaked  and  crumbled,  as  you  see,  it  will  then, 
gradually  be  diffused  in  the  water,  and  form  a  pasty  mass.  Were  we  to  con- 
tinue to  add  water,  the  lime  would  at  length  be  dissolved  in  it,  and  entirely 
disappear,-  but  for  this  purpose  it  requires  no  less  than  700  times  its 
weight  of  water.  This  solution  is  called  lime-tvater(7). 

Caroline.     How  very  small,  then,  is  the  proportion  of  lime  dissolved! 

Mrs  B.  The  liquid  contained  in  this  bottle  is  lime-water:  it  19  often 
used  as  a  medicine,  chiefly,  I  believe,  for  the  purpose  of  combining  with, 
and  neutralizing,  the  superabundant  acid  which  it  meets  with  in  the  stomach. 

Emily.  I  am  surprised  that  it  is  so  perfectly  clear:  it  does  not  at  all 
partake  of  the  whiteness  of  the  lime. 

Mrs  B.  Have  you  forgotten  that,  in  solutions,  the  solid  body  is  so  mi- 
nutely subdivided  by  the  fluid  as  to  become  invisible,  and,  therefore,  will 
not,  in  the  least  degree,  impair  the  transparency  of  the  solvent? 

The  attraction  of  lime  for  carbonic  acid  is  so  strong,  that  it  will  absorb 
it  from  the  atmosphere.  We  may  see  this  effect  by  exposing  a  glass  of  lime- 
water  to  the  air:  the  lime  will  soon  separate  from  the  water,  and  form  a 
•white  film  upon  the  surface,  which  is  carbonate  of  lime y  and  perfectly  simi- 
lar to  common  chalk(8). 


4.  Of  what  are  the  earths  said  to  form  constituent  parts? 

5.  What  is  observed  on  the  subject  of  lime  and  its  carbonate? 

6.  What  is  meant  by  quicklime,  and  what  effect  does  water  produce  upon  it? 

7.  If  more  water  is  added,  what  would  eventually  occur? 

8.  What  is  lime-water,  and  what  effect  has  air  upon  it? 

P  2 


174  CONVERSATIONS  ON  CHEMISTRY. 

Caroline.  The  white  film  begins  already  to  appear  on  the  surface  of  tho 
water;  but  it  is  far  from  resembling  hard  solid  chalk. 

Mrs  B.  That  is  owing  to  its  extreme  tenuity:  in  a  little  time  it  will 
collect  into  a  more  compact  mass,  Avhen,  upon  the  slightest  agitation,  the 
film  will  break  and  subside  to  the  bottom  of  the  glass. 

If  you  breathe  through  lime-water,  the  carbonic  acid,  which  is  mixed 
with  the  air  that  you  expire,  will  produce  a  similar  effect.  It  is  an  experi- 
ment very  easily  made: — I  will  pour  some  lime-water  into  this  wine-glass, 
and,  by  breathing  repeatedly  through  it  by  means  of  a  glass  tube,  you  will 
soon  perceive  a  milky  appearance  in  the  water,  and  a  precipitation  of  car- 
bonate of  lime. 

Emily.    I  see  already  a  small  white  cloud  formed. 

Mrs  B.  It  is  composed  of  minute  particles  of  chalk:  these  at  present 
float  in  the  water,  but  they  will  soon  subside(9). 

Carbonate  of  lime,  you  see,  is  insoluble  in  water,  since  the  lime  which 
was  dissolved  reappears  when  converted  into  a  carbonate;  but  you  must 
take  notice  of  a  very  singular  circumstance,  which  is,  that  chalk  is  soluble 
in  water  highly  impregnated  with  carbonic  acid. 

Caroline.  It  is  very  curious,  indeed,  that  carbonic  acid  gas  should  ren- 
der lime  soluble  in  one  instance,  and  insoluble  in  the  other! 

Mrs  B.  I  have  here  a  bottle  of  soda  water,  which,  you  know,  is  strong- 
ly impregnated  with  carbonic  acid;  let  us  pour  a  little  of  it  into  a  glass  ot 
lime-water.  You  see  that  it  immediately  produces  a  precipitation  of  car- 
bonate of  lime. 

Emily.     Yes,  a  white  cloud  appears. 

Mrs  B.  I  will  now  pour  an  additional  quantity  of  the  soda  water  into 
the  lime-water. — 

Emily.  How  singular!  The  cloud  is  re-dissolved,  and  the  liquid  is  again 
transparent(lO). 

Mrs  B.  The  mystery  will  disappear,  if  it  be  admitted  that  the  carbonate 
of  lime  is  soluble  in  carbonic  acid, whilst  it  is  insoluble  in  water.  The  first 
portion  of  carbonic  acid,  which  I  introduced  into  the  lime-water,  was  all 
employed  in  forming  the  carbonate,  and  of  course  there  was  none  left  to  dis- 
solve it,  but  an  additional  quantity  of  carbonic  acid  effected  its  solution(ll).  ; 

Caroline.  That  is  easily  understood,  and  quite  satisfactoi'y.  You  for- 
merly mentioned  that  marble  was  a  species  of  lime-stone,  and  I  know  that, 
in  some  places,  it  is  burnt  in  kilns  to  make  quicklime.  I  have  likewise 
p06B  oyster-shells  used  for  the  same  purpose:  are  they  too  carbonate  of  lime? 
Mrs  B.  They,  and  the  shells  of  other  fishes,  consist  principally  of  carbo- 
nate of  lime,  but  also  contain  phosphate  of  lime:  they  are  therefore  less  pure, 
and  make  a  weaker  mortar  than  most  of  the  lime-stones(12).  You  are  i 
aware  that  the  mortar  and  plaster  used  in  building  consist  of  quicklime  and 
sand.  These  two  substances  gradually  harden,  and,  in  the  lapse  of  years, 
become  like  stone.  It  is  for  this  reason  that  the  mortar  is  extremely  hard  in 
old  buildings:  in  them  the  lime  has  gradually  been  reconverted  into  a  car-  j 
bonate  by  absorbing  the  carbonic  acid  of  the  atmosphere(lS). 

Emily.  Is  not  plaster  of  Paris  a  kind  of  lime?  I  know  it  is  used  with 
water  much  in  the  same  way,  when  the  plaster  figures  are  made  of  it. 

Mrs  B.  Plaster  of  Paris  is  a  sulphate  of  lime,  which  is  found  in  great 
abundance  in  many  places.  The  city  of  Paris  is  almost  entirely  built  of, 


9.   Detail  the  experiment  of  breathing  through  lime  water. 

10.  What  is  the  fact-respecting  the  solubility  of  carbonate  of  lime? 

11.  In  what  way  is  this  accounted  for? 

12.  What  is  said  respecting  marble  and  the  shells  of  fishes? 

13.  What  occasions  the  hardness  of  mortar  in  old  buildings? 


ON  THE  EARTHS.  175 

and  founded  upon  it,  and  from  that  place  it  has  derived  its  most  common 
name,  but  it  is  also  called  gypsum.  In  preparing  it  to  be  used  as  a  cement, 
or  mortar,  or  for  making  plaster  casts,  it  is  heated,  which  separates  a  quan- 
tity of  water  from  it,  but  does  not  drive  off  its  acid.  When  this  calcined 
plaster,  as  it  is  called,  is  mixed  up  with  a  quantity  of  water  sufficient  to 
give  it  the  consistence  of  cream,  it  may  be  poured  into  moulds,  and  will 
harden  into  a  kind  of  stone  in  a  very  few  minutes(l4). 

Caroline.  But  what  becomes  of  all  the  water  in  this  case;  it  cannot  dry 
so  rapidly? 

Mrs  B.  Do  you  not  recollect  the  fact  as  regards  lime,  that  water  com- 
bines with  it,  forms  &  hydrate,  and  becomes  solid?  Such  is  the  case  with  the 
sulphate  of  lime;  there  is  a  true  chemical  combination  between  it  and  the 
water,  just  as  there  is  in  lime-stone,  and  in  a  large  number  of  other 
solids(15). 

Emily.  Are  the  carbonic  and  sulphuric  acids  the  only  ones  with  which 
lime  is  naturally  combined  in  the  earth? 

Mrs  B.  No,  but  there  is  only  one  other,  which  we  shall  examine,  and 
that  not  at  present;  it  is  the  beautiful  Derbyshire  spar,  which  is  a  Jluate  of 
lime.  This  and  some  other  combinations  of  lime  remain  to  be  noticed  in 
their  proper  places. 

Caroline.  1  have  seen  lime,  oyster  shells,  and  plaster  of  Paris  spread 
over  the  land  to  render  it  fertile.  In  what  way  do  they  operate? 

Mrs  B.  Quicklime,  the  carbonate,  and  the  sulphate  of  lime,  are  each 
employed  as  manures.  The  former  is  supposed  to  render  active  the  inert 
vegetable  matter  which  maybe  in  the  soil,  by  promoting  its  decomposition; 
the  two  latter  appear  to  stimulate  the  plants,  as  they  enter  into  their  sub- 
stance, and  can  be  detected  in  them  by  chemical  analysis.  We,  however,  are 
much  better  acquainted  with  the  fact  of  their  promoting  vegetation,  than  we 
are  with  the  cause  of  their  doing  so(l6). 

Caroline.  I  am  not  quite  certain,  but  I  believe  you  informed  us  that 
lime  had  been  decomposed. 

Mrs  B.  It  has;  and  it  yielded  oxygen,  and  a  white  metal  with  the  lustre 
of  silver,  to  which  has  been  given  the  name  of  CALCIUM,  lime  itself  being 
known  by  that  of  calcareous  earth.  This  metal  has  been  obtained  in  very 
small  quantities  only,  and  cannot  be  preserved,  as  its  affinity  for  oxygen 
causes  it  to  combine  with  it  very  rapidly  when  exposed  to  the  atmosphere, 
and  thereby  to  reproduce  oxide  of  calcium,  that  is,  quicklime(17). 

I  shall  now  say  a  few  words  about  baryta,  or  barytes  as  it  is  more  fre- 
quently called. 

Emily.  May  I  not  repeat  the  question  put  by  Caroline,  when  you  were 
treating  of  the  alkalies,  and  ask,  if  it  would  not  be  better  to  reject  one  of  the 
names  which  you  have  mentioned,  so  as  to  preserve  uniformity  in  this  respect? 
Mrs  B.  The  attempts  at  producing  uniformity,  have  actually  introduced 
diversity,  as  names  long  used  are  not  easily  changed.  It  has  been  thought 
that  the  names  of  the  alkalies  and  earths  ought  to  have  a  similar  termination, 
and  that  in  a,  has  been  preferred:  hence  potassa,  for  potash;  baryta  for  ba- 
rytes; and  so  of  all  the  others,  with  the  exception  of  lime,  which  would  not 
conform  to  this  arrangement  without  offering  too  great  violence  to  a  word  so 
familiar.  As  this  termination  in  a  is  not  uniformly  followed,  I  shall  occa- 
sionally use  the  more  common,  as  well  as  the  more  systematic  names(18). 


14.  What  is  plaster  of  Paris,  and  how  is  it  prepared  and  used? 

15.  What  becomes  of  the  water  with  which  it  is  mixed? 

16.  What  is  said  of  the  use  of  lime  as  a  manure? 

17.  Has  lime  been  decomposed,  and  of  what  does  it  consist? 

18.  What  is  said  of  the  nomenclature  of  the  earths'? 


176  CONVERSATIONS  ON  CHEMISTRY. 

BARYTES  is  very  nearly  allied  to  lime  in  its  properties.  In  the  form  of  a 
sulphate  it  is  a  pretty  abundant  mineral;  in  that  of  a  carhonate  it  is  but 
sparingly  diffused.  It  is  remarkable  for  its  great  weight,  which  acquired  for 
it  its  former  name  of  terra  ponderosa,  or  heavy  earth. 

It  can  be  rendered  caustic,  and  will  slake  like  lime;  but  is  much  more  sol- 
uble than  that  earth,  -water  taking  up  about  one  twentieth  of  its  own  weight. 
Its  solution,  and  that  of  its  salts  are  virulent  poisons(19). 

JSarytic  -water,  that  is  a  solution  of  baryta  in  water,  is  kept  as  a  test  by  the 
chemist.  It  forms  an  insoluble  salt  with  carbonic  acid,  and  has  so  strong  an 
affinity  for  it  that  it  will  separate  it  from  nearly  all  its  combinations.  A  drop 
of  this  water  when  let  fall  into  a  carbonate  in  solution  will  instantaneously 
produce  a  white  cloud  of  carbonate  of  barytes(20). 

Another  alkaline  earth  was  discovered  some  years  ago,  at  a  place  called 
Strontian,  in  Scotland,  whence  it  is  called  STRONTIA,  or  STRONTITES.  It  so 
strongly  resembles  barytes  in  its  properties,  is  so  sparingly  found  in  nature, 
and  of  so  little  use  in  the  arts,  that  it  will  not  be  necessary  to  enter  into  any 
particulars  respecting  it.  One  of  the  remarkable  characteristic  properties  of 
strontites  is,  that  its  salts,  when  dissolved  in  spirit  of  wine,  and  the  liquid 
set  on  fire,  communicate  to  the  flame  a  tinge  of  a  deep  red,  or  blood  colour. 
In  its  native  state  it  exists  either  as  a  sulphate,  or  a  carbonate.  It  is  poi- 
sonous, but  less  so  than  barytes(21). 

Both  baryta  and  strontia  have  been  made  to  yield  metallic  bases,  re- 
spectively called  BARIUM,  and  STRONTIUM.  Both  greedily  absorb  oxygen  and 
return  to  the  state  of  oxides(22). 

Caroline.  I  confess,  Mrs  B.,thatl  do  not  find  the  history  of  the  earths 
half  so  entertaining  as  that  of  the  simple  substances,  and  their  combina- 
tions. 

•Mrs  B.  I  presume  not,  but  recollect  that  the  beneficial  object  of  our 
meeting  is  not  entertainment,  but  instruction;  and  that  however  desirable  it 
may  be  to  combine  the  two,  the  latter  must  never  be  sacrificed  to  the  for- 
mer. The  earths  form  the  basis  of  so  many  interesting  and  important  com- 
pounds, that  to  omit  them  would  be  to  leave  a  veil  over  other  parts  of  the 
science  of  chemistry,  which  would  render  them  completely  obscure. 

The  next  earth  to  be  considered  is  MAGNESIA. 

Caroline.  I  am  already  pretty  well  acquainted  with  that  earth,  from  its 
use  as  a  medicine. 

•Mrs  B.  It  is  employed  medicinally  both  in  the  state  of  a  carbonate,  and 
in  that  usually  called  calcined  magnesia.  It  is  then,  in  fact,  simple  magne- 
sia; the  water  and  carbonic  acid  having  been  driven  off  from  the  carbonate 
by  heat.  This  earth  is  very  insoluble,  requiring  2000  times  its  weight 
of  water  to  dissolve  it;  but  with  most  acids  it  forms  extremely  soluble  salts. 
It  has  not  so  great  an  attraction  for  acids  as  lime  has,  and  consequently 
yields  them  to  the  latter.  It  is  found  in  a  great  variety  of  mineral  combina- 
tions, such  as  slate,  mica,  amianthus,  soap-stoae,  and  in  certain  lime-stones, 
to  which  it  imparts  peculiar  qualities.  It  does  not,  like  lime,  attract  and 
solidify  water;  but  when  mixed  with  water  and  exposed  to  the  atmosphere, 
it  slowly  absorbs  carbonic  acid  from  the  latter,  and  is  thus  reconverted  into 
a  carbonate.  Its  chief  use  in  medicine  is,  like  that  of  lime,  derived  from  its 
readiness  to  combine  with,  and  neutralize,  the  acid  which  it  meets  with  in 
the  stomach(23). 


19.  What  is  the  nature,  and  what  the  properties  of  barytes} 

20.  Of  what  is  barytic  water  a  delicate  test? 

21.  What  other  earth  strongly  resembles  baryta? 

22.  What  is  the  constitution  of  these  two  earths? 
£3.  What  is  said  of  magnesia  and  its  properties? 


ON  THE  EARTHS.  177 

Emily.  Yet,  you  said  that  it  was  frequently  taken  in  the  state  of  carbo- 
nate, in  which  case  it  is  already  united  with  an  acid;  how  then  can  it  neu- 
tralize the  acid  in  the  stomach? 

Mrs  B.  Because  the  carbonic  acid  stands  so  low  in  the  order  of  affinities, 
that  it  will  yield  the  magnesia  to  any  of  the  others.  It  is,  however,  now 
most  commonly  taken  in  its  calcined  state;  as  it  is  not,  like  lime,  rendered 
caustic  by  calcination.  Combined  with  sulphuric  acid,  magnesia  forms  ano- 
ther and  more  powerful  medicine,  commonly  called  Epsom  salt. 

Caroline.  And  properly,  sulphate  of  magnesia.  Pray,  how  did  it  ob- 
tain the  name  of  Epsom  salt? 

Mrs  B.  Because  there  is  a  spring  in  the  neighbourhood  of  Epsom,  in 
England,  which  contains  this  salt  in  great  abundance,  and  from  which  it 
was  originally  procured.  It  is  now,  however,  extensively  manufactured  from, 
minerals  which  contain  magnesia;  and  also  from  the  water  of  the  ocean,  in 
•which  it  is  always  found(24). 

Magnesia  is  decomposed  with  difficulty,  but  Sir  Humphry  Davy  succeed- 
ed in  procuring  a  minute  portion  of  its  base,  which  exhibited  metallic  pro- 
perties, and  received  the  name  of  Magnesium. 

You  are  aware,  I  believe,  of  what  the  chemist  means  by  SILICA,  or  SILEX. 

Caroline.  I  understand  the  term  silex,  to  be  synonymous  with  sand;  but 
still  it  does  not  seem  that  sand  can  be  a  pure,  individual  earth,  as  any  pul- 
verized hard  stone  would  assume  the  appearance  of  sand. 

Mrs  B.  Although  what  is  commonly  called  sand  is  not  pure  silex,  yet 
that  which  is  found  in  the  beds  of  our  rivers,  and  on  the  sea  shore,  is  nearly 
so.  The  other  earths,  being  lighter,  are  washed  out  from  the  silex;  or 
from  being,  to  a  certain  extent,  soluble  in  water,  are  gradually  dissolved(25). 

Silex,  or  Silica,  abounds  in  rock-crystal,  flint,  sand,  sand-stone,  agate, 
jasper,  cornelian,  and  many  other  minerals,  and  it  forms  the  basis  of  some  of 
the  precious  stones.  It  is  rough  to  the  touch,  and  so  hard  that  it  scratches  and 
wears  away  glass,  metals,  and  stones.  It  is  not  soluble  in  water,  nor  is  it  ac- 
ted upon  by  any  acid  excepting  the Jluoric(^). 

Emily.  Pray  what  is  the  true  colour  of  silex,  which  forms  such  a  variety 
of  different  coloured  substances?  Sand  is  broAvn,  flint  is  nearly  black,  and 
precious  stones  are  of  all  colours. 

Mrs  B.  Pure  silex,  such  as  is  found  only  in  the  chemist's  laboratory,  is, 
like  the  other  earths,  perfectly  white;  and  the  various  colours  which  it  as- 
sumes in  the  different  substances  you  have  just  mentioned,  proceed  from 
the  different  ingredients  with  which  it  is  combined  in  their  formation. 

Caroline.  I  wonder  that  silex  is  not  more  valuable,  since  it  forms  the 
basis  of  some  of  the  precious  stones. 

Mrs  B.  You  must  not  forget  that  the  value  we  set  upon  precious  stones 
depends  in  a  great  measure  upon  their  rarity;  for,  were  those  productions 
either  common,  or  perfectly  imitable  by  art,  they  would  no  longer,  not- 
withstanding their  beauty,  be  so  highly  esteemed.  But  the  real  value  of 
silicious  earth,  in  many  of  the  most  useful  arts,  is  very  extensive.  Mixed 
•with  clay,  it  forms  the  basis  of  all  the  various  kinds  of  earthenware,  from 
the  most  common  utensils,  to  the  most  refined  ornaments  of  china  or  por- 
celain. 

Emily.  And  we  must  recollect  its  importance  in  the  formation  of  glass 
•with  potash  and  with  soda,  which  you  incidently  mentioned;  and  likewise  its 
use  in  giving  hardness  to  mortar,  and  other  cements(27).  I  hope  that 


24.  What  is  Epsom  salt,  and  how  is  it  procured? 

25.  What  is  intended  by  silica,  or  silex? 

26.  In  what  is  it  contained,  and  in  what  is  it  soluble? 

27.  What  is  mentioned  respecting  the  various  uses  of  silex? 


178  CONVERSATIONS  ON  CHEMISTRY. 

, 

before  vre  dismiss  silex,  we  shall  learn  something  further  respecting  glass. 
Notwithstanding  it  is  so  common,  I  always  look  at  it  not  only  as  one  of 
the  most  curious,  hut  also  as  among  the  most  beautiful  productions  of  art. 

JWr*  B.  The  process  by  which  glass  is  formed  is  called  vitrification, 
and  is  not  peculiar  to  mixtures  of  silex  with  potash  and  soda.  Nearly  all 
the  earths  and  metallic  oxides  may,  when  mixed  with  each  other,  be  fused, 
and  converted  into  different  species  of  glass.  You  must  have  noticed  that 
in  the  burning  of  bricks  in  a  kiln,  their  ends  are  frequently  fused,  and  have 
an  appearance  very  similar  to  that  of  green  bottle  glass.  Brick-clay,  and 
indeed  nearly  every  kind  of  earth  which  we  call  clay,  consists  of  a  mixture 
of  silex  and  alumine,  that  is,  of  sand  and  clay,  and  the  vitrification  is  a  con- 
sequence of  this  mixture(28). 

Caroline.  Would  not  the  fusion  take  place  if  the  clay  was  quite  pure, 
•without  the  mixture  of  any  sand? 

Mrs  B.  By  no  means.  It  is  a  property  of  the  pure  earths  not  to  fuse 
in  the  heat  of  any  common  furnace;  although,  when  mixed  with  each  other, 
they  will  melt,  and  form  substances  of  the  nature  of  glass(29). 

Emily.  From  what  can  that  arise  ?  I  suppose  that  it  must  be  from  the 
attraction  they  have  for  each  other,  which  is  rendered  effectual  by  the  heat. 

J\frs  B.  That  is  undoubtedly  the  cause.  By  the  aid  of  oxygen  gas  a 
sufficient  degree  of  heat  can  be  produced  to  fuse  silex;  and  when  mixed  in 
due  proportions  with  potash,  or  with  soda,  it  readily  melts  hi  a  common 
furnace,  combines  with  them,  and  forms  such  glass  as  we  use  in  our  win- 
dows. About  three  parts  of  clean  white  sand,  and  one  of  potash,  or  of  soda, 
answer  the  purpose(30). 

Flint  glass  contains  a  portion  of  oxide  of  lead.  Glass  beads,  and  other  co- 
loured glasses,  receive  their  tinge  from  the  oxides  of  the  different  metals. 
What  we  call  enamel,  is  glass  differently  coloured,  and  rendered  either 
opake,  or  transparent,  by  the  mixture  of  different  oxides  with  the  other  ma- 
terials^! ). 

Caroline.  The  blowing  of  glass,  which  I  have  seen  several  times,  ap- 
pears not  only  curious,  but  absolutely  wonderful.  The  simplicity  of  the  tools' 
employed,  and  the  facility  with  which  the  glass  is  made  to  assume  any  de- 
sired form,  give  to  the  whole  operation  an  air,  I  was  going  to  say,  of  magic. 

Mrs  B.  It  is  certainly  a  business  of  great  apparent  simplicity,  as  well 
as  of  much  real  address  and  manual  skill.  Glass,  when  in  fusion,  has  a  tex- 
ture very  much  like  that  of  melted  sealing-wax.  You  may  readily  blow  the 
latter  into  bubbles  by  melting  it  upon  the  end  of  a  tobacco  pipe  stem,  and 
then  blowing  through  the  tube;  and  you  know  the  facility  with  which  heated 
wax  receives  any  form,  or  impression.  But  we  must  not  dwell  longer  on 
this  subject(32). 

Emily.  You  have  not  told  us  any  thing  respecting  the  decomposition  of 
silex;  is  it,  like  the  other  earths,  a  metallic  oxide? 

J\frs  B.  The  character  of  silex  is  quite  equivocal,  and  chemists  are  not 
at  all  agreed  as  regards  its  nature.  Some  have  classed  it  among  the  acids, 
because  it  combines  with  the  alkalies;  but  this  opinion  seems  to  rest  upon 
too  slender  a  basis  to  justify  its  adoption.  Glass,  according  to  this  opinion, 
would  be  classed  with  the  salts,  as  a  silicate  of  potash,  or  of  soda(33). 

In  the  attempts  to  decompose  siiex,  a  deep  nut  brown  substance  has  been 


28.  What  is  observed  respecting  the  formation  of  glass? 

29.  Are  the  pure  earths  of  difficult  fusibility? 
SO.   Of  what  articles  does  window-glass  consist? 

31.  What  is  said  of  the  composition  of  flint  and  of  coloured  glasses? 

32.  What  remarks  are  made  concerning  the  blowing  of  glass? 

33.  HOW  has  silex  been  classed  by  some  chemists? 


ON  THE  EARTHS.  179 

obtained,  which  has  been  called  SILICON.  It  possesses  no  claim  to  be  ranked 
•with  the  metals,  as  it  is  without  lustre,  does  not  burn  in  oxygen  gas,  and  is 
not  a  conductor  of  electricity. 

Caroline.  Then  at  present  we  must  be  content  to  know  what  silex  assists 
to  make,  and  leave  to  future  discovery  a  knowledge  of  the  articles  of  which 
it  is  itself  composed(34). 

Mrs  B.  AruMiJr A,  or  AX-UMrwE;  called  also  argil  and  argillaceous  earth, 
is  that  substance  which  communicates  the  character  by  which  the  various 
kinds  of  clay  are  distinguished  from  the  other  earths.  The  name  alumine 
is  derived  from  alum,  a  salt  of  which  it  forms  the  base,  and  from  Avhich  it 
may  be  readily  separated  in  a  pure  state(35). 

Alumine  is  contained  in  a  great  number  of  minerals,  but  is  found  chiefly 
in  clay,  mixed  with  silex,  and  usually  coloured  by  the  oxides  of  some  of 
the  metals.  In  its  pure  state  it  is  soft  to  the  touch,  makes  a  paste  with  wa- 
ter, and  hardens  in  the  fire;  which  properties  you  perceive  that  it  retains  in 
its  state  of  mixture.  It  is  impervious  to  water,  and  from  this  circumstance 
is  one  of  the  most  useful  of  the  minerals.  The  beds  of  our  lakes  and  rivers 
are  formed  of  clay,  and  thus  their  waters,  whiifV  would  percolate  through 
sand,  and  all  other  earthy  materials,  are  retained.  By  its  means,  water  is  ac- 
cumulated in  the  caverns  of  the  earth,  producing  those  reservoirs  whence 
issue  the  springs,  which  spout  out  upon  its  surface(36). 

Caroline.  Then  it  is  for  this  reason  that  clay  was  brought  from  a  consi- 
derable distance  to  line  the  bottom  and  sides  of  the  canal,  where  it  passed 
through  a  sandy  soil. 

Mrs  B.  Yes,  and  this  process  is  called  puddling.  Sometimes  puddling  is 
j  necessary  for  many  miles  together,  and  is  essential  to  the  value  of  the  work, 
|  «s  without  it  the  water  would,  in  some  places,  sink  away  as  fast  as  it  could 
be  let  in. 

From  this  retentive  property,  as  regards  water,  clay  is  an  important  ingre- 
dient in  sandy,  loose  soils;  as  it  retains  a  sufficient  portion  of  water  to  render 
them  fertile(37). 

Alumine  is  the  basis  of  every  kind  of  pottery,  entering  into  the  composi- 
tion of  brick,  as  well  as  that  of  the  finest  porcelain.  The  addition  of  silex 
!  hardens  it,  renders  it  susceptible  of  a  degree  of  vitrification,  and  makes  it 
perfectly  fit  for  its  various  purposes.  Indeed  without  this,  the  clay  would 
contract  so  greatly  in  baking  that  the  articles  made  would  lose  their  form. 
The  silex  is  said  to  give  them  body. 

Caroline.  I  can  scarcely  conceive  that  bricks  and  china  should  be  made 
of  the  same  materials. 

Mrs.  B.  Bricks  consist  almost  entirely  of  baked  clay;  the  clays  used 
containing  a  large  portion  of  coarse  sand  in  a  state  of  mixture.  But  to 
the  clays  used  in  the  formation  of  earthen  or  stone  ware,  a  portion  of  silex 
is  usually  added.  For  porcelain,  or  china,  the  Chinese  use  a  mixture  of 
two  earths,  called  by  them  petuns4^  and  kaolin.  Similar  earths  are  found 
both  in  this  country  and  in  Europe,  and  very  fine  porcelain  manufactured 
from  it.  The  materials  are  essentially  the  same  as  for  the  coarse  kind  of 
ware,  but  they  are  in  a  more  pure  and  a  finer  state.  Porcelain  owes  its 
beautiful  semi-transparency  to  the  commencement  of  vitrification(38). 

Emily.  But  the  commonest  earthenware,  though  not  transparent,  is  co- 
vered with  a  kind  of  glazing. 


34.  What  is  remarked  respecting  its  decomposition? 

35.  What  is  alumina,  and  what  are  its  other  names? 

36.  What  is  said  of  its  combinations  and  properties? 

37.  Clay  is  retentive  of  moisture;  what  is  said  respecting  this? 

38.  What  is  remarked  respecting  pottery  and  porcelain? 


180  CONVERSATIONS  ON  CHEMISTRY. 

Mrs  B.  That  is  as  necessary  to  the  use  as  to  the  beauty  of  the  ware, 
as  it  would  be  liable  to  be  spoiled  and  corroded  by  a  variety  of  substan- 
ces, if  not  covered  with  a  coating  of  this  kind.  In  porcelain  it  consists  of 
a  fine  white  glass,  formed  of  such  materials  as  are  susceptible  of  vitrifica- 
tion. The  glazing  of  common  earthenware  is  made  chiefly  of  oxide  of  lead, 
or  sometimes  merely  of  salt,  which,  when  thinly  spread  over  earthen  ves- 
sels, will,  at  a  certain  heat,  combine  with  a  portion  of  the  earthy  material, 
and  run  into  glass(39). 

Caroline.  And  of  what  nature  are  the  colours  which  are  used  for  paint- 
ing on  porcelain? 

Jlfrs  Ji.  They  are  all  composed  of  metallic  oxides;  so  that  these  colours, 
instead  of  receiving  injury  from  the  application  of  fire,  are  strengthened  and 
developed  by  its  action,  which  causes  them  to  undergo  different  degrees  of 
oxidation,  according  to  their  natures(40). 

Alumine  and  silex  are  not  only  often  combined  by  art,  but  they  have  in 
nature  a  very  strong  tendency  to  unite,  and  are  found  contained,  in  different 
proportions,  in  various  gems  and  other  minerals.  Indeed,  many  of  the  pre- 
cious stones,  such  as  the  sJiby,  oriental  sapphire,  and  other  oriental  gems, 
consist  chiefly  of  alumine(4l). 

Emily.     Is  alumine  known  to  be  a  metallic  oxide? 

Mrs  B.  It  has  been  proved,  unequivocally,  to  be  an  oxide;  and  the  ALTJ- 
MiNtrM  obtained  from  it  exhibited  some  of  the  metallic  characteristics.  It 
was  in  the  form  of  a  grayish  powder,  difficult  of  fusion;  but  in  oxygen  gas  it 
burnt  very  brilliantly,  and  produced  alumine(42). 

Emily.  The  other  four  earths  you  spoke  of  as  being  very  rarely  found, 
a"nd  I  suppose  therefore  that  but  little  is  known  of  their  properties. 

J\frs  B.  ZIRCONIA  has  been  discovered  in  a  precious  stone  called  zircon 
or  jargon,  from  Ceylon:  it  has  also  been  found  in  the  hyacinth.  GLUCINA  is 
found  in  the  beryl  and  the  emerald;  YTTRIA,  in  two  or  three  minerals 
frorh  Ytterby  in  Sveden,  but  not  in  any  others.  THORINA,  in  one  mineral 
only,  in  Norway.  The  experiments  performed  upon  them  have  furnished 
satisfactory  indications  that  they  are  all  of  them  oxides(43). 

Caroline.     There  is   a  kind  of  stone  which  has  excited  much  attention, 
and  respecting  which  I  should  like  to  learn  something.     Whether  it  may  be  - 
placed  among  the  earths  or  not,  I  cannot  tell,  as  it  appears  to  belong  to  the 
heavens,  or  to  some  other  world  than  this:  1  mean  the  stones  which  have,  in 
so  many  instances,  been  known  to  fall  from  the  atmosphere,  or  elsewhere. 

J\frs  B.     These  meteorolites,  or  meteoric  stones,  have  completely  puzzled 
the   philosophers,  and  will  probably   continue  to   do  so.     Even  the  fact  of 
their  having  fallen  was  disputed  for  ages,  although  attested  most  satisfacto- 
rily in  the  records  of  ancient  and  modern  times.     In  most  instances  their 
fall  has  been  preceded  by  a  fiery  meteor,  and  a  loud  explosion;  immediately 
after  which  they  have  been  seen  to  descend,  some  times  singly,  and  at  others 
in  considerable  numbers,  and  extending  over  a  large   space.     When  the 
have  been  examined  soon  after  their  fall,  they  have  always  been  found  hot 
There  is  a  remarkable  similarity  in  their  composition,  in  whatever  quarte 
of  the  globe,  and  at  whatever  period  of  time,  they  may  have  fallen.     Anothe 
curious  circumstance  distinguishes  them,  and  that  is  they  do  not  resembl 


39.  How  is  the  glazing  of  these  articles  effected? 

40.  What  colours  are  used  in  painting  on  porcelain? 

41.  Mention  some  of  the  natural  combinations  of  alumine. 

42.  What  information  have  we  concerning  its  composition? 

43.  What  is  observed  respecting  the  remaining  earths? 


ON  THE  METALS  IN   GENERAL.  181 

.  either  of  the  known  mineral  substances  on  the  face  of  the  globe,  although 
all  the  materials  of  which  they  consist  are  familiar  to  us(44). 

Emily.     And  of  what  substances  are  they  composed? 

Mrs  B.  Their  earthy  matter  consists  of  silex  and  magnesia,  and  they 
contain  iron,  in  a  native  state,  in  the  form  of  oxide,  and  in  that  of  a  sulphu- 
ret.  This  iron  is  always  accompanied  by  another  and  a  rare  metal,  called 
chrome,  and  generally  with  a  considerable  portion  of  a  third,  named 
nickel(45). 

Caroline.  I  suppose  that  we  might  as  well  inquire  of  the  poets  as  of  the 
philosophers,  how  these  stones  are  formed,  and  whence  they  come;  as  the 
philosopher,  to  obtain  his  answer,  would  have  to  invade  the  province  of  the 
poet,  and  mount  into  the  airy  regions  of  imagination. 

Mrs  B.  Some  have  supposed  that  they  are  ejected  from  volcanos  in  the 
moon,  with  a  force  which  brings  them  within  the  sphere  of  the  earth's  attrac- 
tion. Others  have  imagined  that  the  materials  of  which  they  are  composed 
are  volatilized  by  some  mysterious  process;  that  in  their  combination  in  the 
atmosphere  they  form  the  fiery  meteors  which  precede  their  explosion;  and 
that  their  heat  originates  in  the  condensation  of  their  vaporized  constituents. 
Fancy  has  also  created  little  globes,  revolving  round  our  earth,  within  the 
sphere  of  its  attraction,  but  too  far  off,  and  too  small,  to  be  visible.  The 
collision  or  bursting  of  these  terrellas,  or  little  earths,  has  been  thought  to 
explain  the  phenomenon(46).  Either  of  these  opinions,  when  investigated, 
appears  to  be  fraught  with  insurmountable  difficulties,  which  I  will  not  in- 
crease by  any  crude  conjectures  of  my  own  upon  a  subject  which  has  con- 
founded the  wisdom  of  the  wise(47). 


CONVERSATION  XVIII. 

ON  THE  METALS  IN  GENERAL. 

Number  of  Metals  known.  Their  distinguishing  Characteristics.  Ores 
and  native  Metals.  Roasting,  Smelting,  and  general  process  of  Reduction. 
Oxidation  and  Reduction  of  the  perfect  Metals.  Oxidation  and  Solution  by 
Acids,  -with  the  formation  of  Salts.  Nomenclature  of  Metallic  Oxides. 
Alloys  of  Metals.  Malleability  and  Ductility.  Soldering.  Welding. 
Combustibility  of  Metals.  Gas  holder.  Hare's  Oxy-hydrogen,  or  Com- 
pound Blowpipe.  Combustion,  Fusion,  and  Ignition  produced  by  it.  Modi- 
fication of  the  Blowpipe,  by  condensing  the  Gases.  Metallic  Sulphurets 
formed  -with  extrication  of  Light  and  Heat. 

Mrs  B.  The  METALS  contained  in  the  alkalies  and  earths,  were  all  new 
to  you,  and  beside  these  there  are  a  number  of  others,  which,  though  known 
to  the  chemist,  are  so  sparingly  diffused,  or  so  rarely  obtained,  that  you  will 
most  probably  never  see  them.  Those  however  to  which  our  principal  atten- 
tion will  be  given,  are  familiar  to  you,  being  amongst  the  most  useful  as  well 
as  the  most  brilliant  substances  with  which  we  are  acquainted. 

Caroline.  To  say  the  truth,  I  seem  to  be  already  so  well  acquainted  with 
them,  that,  from  further  inquiry,  I  anticipate  but  little  gratification  compared 


44.  State  the  nature  and  the  history  of  meteorolites. 

45.  Of  what  materials  are  they  found  to  consist? 

46.  What  opinions  have  been  entertained  in  regard  to  their  origin? 

47.  What  remark  is  made  concerning  these  opinions? 


182  CONVERSATIONS  ON  CHEMISTRY. 

with  that  which  we  have  received  from  the  contemplation  of  some  of  those 
mysterious  and  intangible  heings,  of  whose  properties,  and  indeed  of  whose 
very  existence  we  were  previously  ignorant. 

Mrs  B.  There  is  a  great  difference  between  familiarity  with  a  counte- 
nance, and  an  intimate  acquaintance  with  a  character:  we  must  close  our 
•eyes  to  avoid  the  former;  to  acquire  the  latter,  we  must  exercise  some  of  the 
noblest  powers  of  our  nature.  You  have  already  met  with  metals  where  you 
least  expected  to  find  them,  and  acquired  a  knowledge  of  properties  in  them 
of  which  you  could  have  had  no  previous  conception.  The  alkalies  and  the 
earths  have  presented  us  with  a  number  of  such  bodies,  and,  believe  me,  you 
have  yet  much  to  learn  respecting  those  whh  which  you  imagine  yourself  the 
most  familiar.  To  treat  of  them  fully  would  require  more  time  than  we  can 
devote  to  the  whole  subject  of  chemistry,  and  we  must  therefore  confine  our- 
selves to  a  cursory  view  of  their  properties,  whether  examining  them  col- 
lectively or  individually. 

The  whole  number  of  metals  known  to  the  chemist  amounts  to  about  forty. 
Qf  these,  seven  only  were  known  to  the  ancients,  namely,  gold,  silver,  iron, 
copper,  mercury,  lead,  and  tin.  The  others  have  all  been  discovered  since 
the  fifteenth  century (1). 

Emily.  Is  there  any  other  property  by  which  the  metals  are  distinguished 
from  other  bodies,  excepting  that  peculiar  lustre  which  they  exhibit  when 
rubbed  bright,  and,  if  we  are  to  judge  by  this  alone,  may  we  not  sometimes 
be  deceived? 

Mrs  B.  Although  the  metallic  lustre  is  the  principal  immediate  charac- 
teristic of  the  metals,  it  is  by  no  means  the  only  one;  their  distinguishing 
features  are  the  following: 

They  are  all  good  conductors  of  caloric  and  of  electricity.  When  their 
combinations  with  oxygen,  sulphur,  or  similar  substances,  are  submitted  to 
the  action  of  galvanism,  the  metals  are  always  attracted  by  the  negative  pole 
of  the  battery;  and  for  this  reason  they  are  denominated  electro-positive  bodies. 
They  are  in  general  good  reflectors  of  light,  which  arises  from  that  peculiar 
lustre  which  you  have  mentioned,  and  they  are  opake.  Any  substance  pos- 
sessing all  these  properties  may  be  ranked  as  a  metal (2). 

Emily.  You  have  not  mentioned  their  great  weight;  are  (hey  not  the 
heaviest  bodies  in  nature? 

Mrs  _B.  Until  the  discovery  of  the  bases  of  the  alkalies,  great  specific 
gravity  was  ascribed  to  the  metals,  all  those  previously  known  being  heavier 
than  any  non-metallic  substance;  but  the  lightness  of  these  alkaline  bases 
proves  that  this  is  not  an  essential  characteristic  of  the  metals(3). 

A  lustre  resembling  that  of  the  metals  is  sometimes  seen  where  we  are 
convinced  that  Undoes  not  result  from  their  presence.  The  brilliancy  and 
colour  of  gold  and  silver  are  frequently  exhibited  on  the  wings  of  the  moth, 
and  on  the  body  of  the  caterpillar,  as  well  as  on  that  of  some  other  insects. 
There  is  also  a  class  of  mineral  bodies  called  pyrites,  which  possess  a  lustre 
resembling  that  of  the  precious  metals.  These  substances  are  metallic  sulphu- 
rets;  such  as  sulphuret  of  iron,  or  iron  pyrites,  sulphur et  of  copper,  or  cop- 
pa*  pyrites,  and  sulphuret  of  tin,  or  tin  pyrites(4>}. 

Caroline.  But  it  would  seem,  then,  that  these  are  not  exceptions,  as  they 
are  actually  metallic  substances. 

Mrs  JB.  By  heating  these  sulphurets  on  a  hot  coal,  a  portion  cf  the  sul- 
phur is  sublimed,  and  abrown  earthy  mass  alone  remains^  but  although  this 


1.  What  is  said  respecting  the  number  and  the  discovery  of  the  metals? 

2.  What  are  the  distinguishing  characteristics  of  the  metals? 

3.  What  remarks  are  made  on  the  subject  of  their  great  specific  gravity? 

4.  What  articles  possess  a  lustre  resembling  that  of  the  metals? 


ON  THE  REDUCTION  OF  METALS.  183 

mass  contains  the  whole  of  the  metal,  it  is  without  lustre.  It  is  plain,  there- 
fore, that  the  metallic  appearance  is  derived  from  the  presence  of  the  sulphur; 
or  rather  from  the  peculiar  combination  of  the  sulphur  and  the  metal. 

Caroline.  The  ores  of  many  of  the  metals  appear  very  beautiful  in  ea- 
binets  of  minerals;  in  what  state  of  combination  do  the  metals  usually  exist 
in  these  ores? 

Mrs  B.  In  a  great  variety  of  states ;  but  they  are  generally  com- 
bined with  oxygen,  sulphur,  earths,  or  acids,  and  there  are  frequently  two 
or  more  different  metals  contained  in  the  same  ore.  The  ores  are  found  near 
the  surface  of  the  earth  in  most  parts  of  the  world,  but  chiefly  in  mountain- 
ous districts,  where  the  ground  has  been  disturbed  by  earthquakes,  volea- 
nos,  and  other  convulsions  of  nature.  '  They  are  usually  spread  in  strata  or 
beds,  called  veins,  and  these  veins  are  composed  of  a  certain  quantity  of  me- 
tal, combined  with  such  articles  as  I  have  named,  which  are  called  mine- 
ralizers.  Thus,  speaking  of  a  sulphuret  of  lead,  we  may  say  that  the  lead 
is  mineralized  by  sulphur.  The  metals,  sometimes,  have  no  mineralizer, 
but  are  found  in  the  pure  metallic  state,  and  are  then  called  native  metsd.s(5}. 

Emily.  These  mineralizers  are  so  different  from  each  other,  that  the 
metals  must  necessarily  be  separated  from  them  by  very  different  methods, 
I  have  often  heard  of  the  roasting  of  ores,  but  do  not  understand  what  is 
meant  by  it,  and  whether  it  is  always  necessary,  and  with  every  kind  of  ore. 

Mrs  J3.  The  process  of  extracting  a  metal  from  its  ores  is  called  HEDUO 
TIOU .  All  that  I  can  give  you  of  the  modes  of  procedure  in  this  operation 
will  be  but  a  faint  outline  of  its  general  principles(6).  Ores  are  roasted, 
to  separate  sulphur,  or  other  volatile  articles  from  them.  Roasting  usually 
consists  in  placing  the  ore  upon  fires  of  wood,  or  coal,  in  the  open  air,  and 
thus  heating  them  to  redness.  But  there  are  many  ores,  particularly  the 
oxides,  which  do  not  require  to  be  roasted(7). 

The  next  operation  is  Called  smelting,  that  is  melting  out  the  metal  from 
the  ore.  For  this  purpose  it  is  put  into  a  furnace  with  charcoal;  the  fuel  and 
the  ore  being  mixed  together.  The  fire  is  then  lighted  and  the  whole 
mass  intensely  heated.  The  affinity  between  oxygen  and  carbon,  when  the 
latter  is  at  a  red  heat,  is  such,  that  if  the  ore  be  an  oxide,  the  carbon  de- 
prives it  of  its  oxygen,  and  brings  it  into  the  metallic  state(8). 

Emily.  You  have  shown  us  that  iron  and  some  other  metals,  when  highly 
heated,  combine  with  oxygen,  and  become  oxides;  I  do  not  see,  therefore, 
how,  by  the  same  operation,  these  same  oxides  should  again  lose  their  oxygen, 
and  become  metals. 

Mrs  B.  The  cases  are  very  different.  When  iron,  lead,  and  many 
other  metals  are  heated  in  atmospheric  air,  they  attract  its  oxygen,  and  be- 
come oxides.  If  they  were  perfectly  surrounded  by  red-hot  charcoal,  this 
would  protect  them  from  oxidation,  in  consequence  of  its  own  superior  affi- 
nity for  oxygen;  and  in  the  process  of  smelting,  the  same  superior  affinity 
of  the  heated  charcoal  enables  it  to  deprive  the  oxides  of  their  oxygen,  and 
thus  to  reduce  them  to  the  metallic  state. 

Caroline.  Then  the  charcoal  not  only  absorbs  the  oxygen  of  the  air 
•which  feeds  the  fire,  but  that  also  which  is  contained  in  the  oxides(9). 

Mrs  B.  It  does,  and  of  course  becomes  converted  into  carbonic  acid. 
Oxide  of  iron  requires  a  heat  too  intense  for  us  to  attempt  to  reduce  it; 
but  we  can  easily  operate  upon  the  oxide  of  lead.  Common  red  lead  is  an 


5.  In  what  combinations  and  situations  are  the  metals  found? 

6.  What  is  meant  by  reduction  as  applied  to  a  metal ' 

7.  What  is  roasting,  and  for  what  purpose  is  it  resorted  to? 

8.  What  is  meant  by  smelting,  and  how  is  it  effected? 

9.  In  what  way  does  charcoal  operate  in  the  process  of  reduction  ? 


184  CONVERSATIONS  ON  CHEMISTRY. 

oxide  of  that  metal,  and  were  we  to  mix  a  portion  of  this  oxide  with  pulver- 
ized charcoal,  grease,  or  any  substance  containing  much  carbon,  and  heat 
them  in  the  fire  in  a  common  tobacco-pipe,  the  lead  would  be  reduced,  and 
might  be  poured  out  in  the  metallic  state(lO). 

Caroline.  That  we  can  very  easily  try,  when  we  have  a  tobacco-pipe;  I 
will  get  one  presently. 

Mrs  B.  We  can  try  a  similar  experiment  immediately,  with  one  of  these 
red  wafers.  Common  red  wafers  consist  of  flour  paste,  coloured  with  red 
oxide  of  lead.  We  need  therefore  only  set  fire  to  the  edge  of  one  of  these 
wafers,  and  hold  it  over  a  sheet  of  white  paper,  when  the  metallic  lead  will 
be  seen  to  fall  upon  the  paper  in  minute  globules. 

Emily.  How  curious,  and  yet  how  simple !  the  globules  are  numerous 
and  quite  distinct.  The  carbon  contained  in  the  flour  has,  in  this  case,  pro- 
duced the  effect  by  combining  with  the  oxygen  of  the  red  lead(ll). 

Caroline.  But  after  the  metals  are  reduced,  and  have  run  down  from 
the  ores  to  the  bottom  of  the  furnace,  below  the  charcoal,  I  should  suppose 
they  would  then  again  become  oxidized. 

Mrs  B.  The  metal  is  then  protected  from  the  action  of  the  air  by  allowing 
its  surface  to  be  covered  with  a  melted  mass  of  earthy  or  alkaline  matter,  which 
when  so  employed  is  called  a.  flux,  because  it  flows  over  the  metal.  Some- 
times the  earthy  matter  contained  in  the  ores  themselves  fuses,  and  formn  a 
glass  which  covers  the  metal.  Potash,  or  other  materials  which  produce  the 
same  effect,  are  frequently  added,  these  additions  being  made  according  to 
the  nature  of  the  metal,  or  of  the  ore  to  be  reduced.  Rosin,  tallow,  or  soap, 
•will  prevent  the  oxidation  of  lead,  by  keeping  it  from  contact  with  the  air, 
•when  melted  in  an  open  vessel  over  the  fire(12). 

Emily.  Do  all  the  metals  when  heated  attract  oxygen  from  the  atmoa- 
phere,  and  become  oxides  ?  I  have  understood  that  they  do  not. 

Mrs  B.  Some  of  the  nvetals  have  but  a  feeble  affinity  for  oxygen,  and  if 
combined  with  it,  part  from  it  very  readily.  The  oxides  of  gold,  silver, 
mercury,  and  platinum,  may  be  reduced  by  heat  alone,  without  the  addition 
of  any  coaly  matter.  Their  oxygen  unites  to  the  caloric,  assumes  the  gase- 
ous form,  and  leaves  the  metal  in  a  pure  state(13). 

Caroline.  The  very  means  therefore  by  which  some  metals  are  oxidized, 
will  separate  the  oxygen  from  those  you  have  just  named,  and  reduce  them 
to  the  state  of  pure  metals.  But  how  can  they  be  made  into  oxides  at  all, 
if  heating  them  in  contact  with  air  will  not  effect  it? 

Mrs  B.  Those  which  cannot  be  oxidized  by  heat  alone,  were  formerly 
called  the  perfect  metals,  a  name  now  nearly  out  of  use.  They  may  be  oxi- 
dized by  sending  through  them  powerful  electric  discharges;  but  for  this 
purpose  they  must  be  reduced  to  the  form  of  fine  wire,  or  of  thin  leaves, 
and  the  oxide  is  obtained  in  but  small  quantities.  All  metals  however  yield 
to  the  oxidating  power  of  some  one  or  more  of  the  acids.  You,  I  am  sure, 
will  recollect  what  you  were  formerly  told  upon  that  subject(l4). 

Caroline.  I  believe  I  do.  I  think  you  informed  us  that  the  acids  and 
the  metals  unite  together  and  form  salts;  or  rather  that  the  acids  unite 
to  the  oxides  of  the  metals  and  form  them,  as,  in  all  eases,  the  metal 
must  be  oxidized  before  it  can  combine  with  the  acid(15). 

Mrs  B.     Yes;  and,  of  course,  if  a  metal  be  put  into  an  acid,  and  then 


10.  How  may  this  be  shown  by  means  of  red  lead? 

11.  How  may  a  wafer  be  made  to  answer  this  end? 

12.  What  sirejluxes,  and  for  what  purpose  are  they  employed? 

13.  What  is  observed  respecting  gold,  silver,  mercury,  and  platinum? 

14.  What  were  such  metals  called,  and  how  may  they  be  oxidized? 

15.  What  is  said  of  the  oxidation  of  metals  by  acids? 


ON  THE  OXIDATION  AND  SOLUTION  OF  METALS.     185 

undergo  solution,  a  double  process  must  be  carried  on.  In  order  to  its  con- 
version into  a  metallic  salt,  the  metal  must  first  be  oxidized,  and  the  oxide 
then  dissolved  by  the  acid.  In  n.aking  hydrogen  by  the  action  of  dilute 
sulphuric  acid  upon  iron,  the  metal,  you  know,  obtained  the  oxygen  from 
the  water,  and  its  hydrogen  was  consequently  liberated;  but  it  more  fre- 
quently happens  in  the  solution  of  a  metal  by  an  acid,  that  the  metal  obtains 
its  oxygen  by  decomposing  a  portion  of  the  acid,  the  oxide  thus  formed 
being  dissolved  by  the  remaining  acid(16). 

Emily.     Then,  in  this  case,  you  do  not  obtain  any  hydrogen  gas? 

Mrs  B.  Certainly  not;  whatever  gas  escapes  must  be  that  which  results 
from  the  decomposition  of  the  acid,  and  must  depend  therefore  upon  the 
composition  of  that  acid  (17). 

In  this  phial  there  is  nitric  acid,  some  of  which  I  am  about  to  pour  over 
the  shreds  of  copper  in  this  glass,  when  a  violent  effervescence  will  take 
place,  and  a  large  quantity  of  gas  will  be  extricated. 

Caroline.  Oh,  what  *a  disagreeable  smell,  and  what  a  deep  orange 
coloured  vapour  escapes!  pray  what  is  that? 

•Mrs  B.  It  is,  like  the  acid  itself,  a  compound  of  nitrogen  and  oxygen, 
but  containing  less  oxygen.  Its  particular  composition  I  shall  hereafter 
explain;  you  can,  however,  form  some  judgment  about  it  when  I  tell  you 
that  it  is  nitrous  acid(18). 

Emily.  The  effervescence  is  now  over.  I  suppose,  therefore,  that  the 
metal  is  both  oxidated  and  dissolved. 

Mrs  B.  Yes.  And  were  we  to  evaporate  the  fluid,  we  should  obtain  the 
salt  called  nitrate  of  copper,  in  the  solid  state;  as  you  see  it  in  this  phial(19). 

Caroline.  Pray,  what  would  have  been  the  consequence,  Mrs  B.,  if 
instead  of  metallic  copper  you  had  put  an  oxide  of  copper  into  the  nitric 
acid?  I  do  not  see  in  this  case  how  any  decomposition  of  the  acid  could 
have  been  effected. 

Mrs.  B.  Your  inference  is  correct:  had  we  put  in  an  oxide  of  copper, 
the  metal  being  already  oxidized,  no  effervescence  would  have  taken  place. 
Nor  would  there  have  been  any  decomposition  of  the  acid;  but  the  oxide 
•would  have  been  quickly  dissolved,  and  the  same  kind  of  salt  produced  as 
in  the  first  solution(SO). 

Emily.  It  seems  rather  strange  that  the  metal  when  put  into  dilute  acids, 
should  sometimes  decompose  them,  and  at  others  decompose  the  water. 

Caroline.  I  think  I  can  trace  the  reason  of  this.  When  the  oxygen  in 
the  acid  is  united  to  its  base  by  an  affinity  less  powerful  than  that  of  oxygen 
for  hydrogen,  the  acid  is  decomposed;  and  when  the  reverse  is  the  fact, 
water  is  decomposed(21). 

Mrs  B.  Your  explanation  is  very  good.  There  are  some  of  the  acids 
•which  have  a  strong  affinity  for  the  oxides  of  some  of  the  metals;  yet,  when 
concentrated,  that  is,  deprived  as  far  as  possible  of  water,  they  will  jiot  act 
upon  the  pure  metals.  This  is  the  case  with  sulphuric  acid  and  iron:  it 
the  acid  be  deprived  of  all  the  water  with  which  it  will  part,  it  will  not  act 
upon  iron,  because  its  oxygen  is  united  to  its  sulphur  by  an  affinity  too 
powerful  for  the  iron  to  overcome(22). 


16.  What  double  action  is  necessary  to  their  conversion  into  salts? 

17.  What  circumstance  will  determine  the  kind  of  gas  given  out? 

18.  Detail  what  is  said  respecting  nitric  acid  and  coppem 

19.  What  is  the  salt  produced,  and  how  is  it  obtained? 

20.  What  would  result  from  putting  oxide  of  copper  into  nitric  acid? 

21.  What  determines  whether  the  acid  or  the  water  shall  be  decom- 
posed? 

22.  What  is  said  respecting  concentrated  acids  and  metals ? 

Q2 


186  CONVERSATIONS  ON  CHEMISTRY. 

Emily-  You  have  taught  us  that  many  of  the  metals  are  capable  of  unit- 
ing to  different  proportions  of  oxygen,  and  that,  from  this  cause,  the  oxides 
differ  very  much  in  their  character.  If  all  these  different  oxides  are  dis- 
solved by  the  acids,  there  must  be  as  many  different  salts  of  each  metal  as 
there  are  oxides(23). 

J\frs  B.  Your  remarks  remind  me  of  what  I  had  intended  to  inform  yon 
respecting  these  different  oxides.  Do  you  recollect  the  names  by  which 
we  distinguish  the  several  oxides  of  the  same  metal  from  each  other? 

Emily.  I  will  endeavour  to  repeat  them  as  I  have  frequently  done  to  my- 
self, in  order  that  I  might  not  forget  them. 

When  a  metal  unites  to  oxygen  in  one  proportion,  it  is  simply  called  an 
oxide.  When  in  two,  the  first  is  called  the  protoxide,  and  the  second  the 
deutoxide,  or  peroxide.  When  in  three,  we  have  the  protoxide,  deutoxide, 
and  tritoxide,  or  peroxide;  and  sometimes  there  is  a  fourth  called  the 
quadroxide.  The  name  peroxide  is  usually  given  to  the  last  of  the  se- 
ries, whatever  may  be  its  number(24). 

Jllrs  B.  Very  good.  In  the  greater  number  of  instances,  acids  unite 
with  the  protoxide  only,  those  which  are  more  highly  oxygenated  being 
altogether  insoluble(25).  Do  you  remember  in  Avhat  way  we  obtained 
oxygen  gas  by  the  action  of  sulphuric  acid? 

Caroline.  You  mixed  it  in  a  retort  with  a  metallic  oxide  which  you 
called  the  black  oxide  of  manganese,  and  then  heated  the  mixture  over  a 
lamp,  when  the  oxygen  escaped.  1  have  frequently  puzzled  myself  to  find 
out  the  source  of  the  oxygen  in  this  instance. 

J\frs  B.  I  think  you  will  be  able  to  discover  it  when  I  inform  you  that 
the  black  oxide  of  manganese  is  the  tritoxide  of  that  metal,  and  that  when  it 
is  mixed  with  the  sulphuric  acid,  and  heat  applied,  a  sulphate  of  manga- 
nese is  formed,  consisting  of  the  acid  combined  with  the  protoxide(26). 

Caroline.  Oh,  yes,  now  I  see  the  operation  plainly.  The  acid  combined 
with  the  protoxide  and  the  excess  of  oxygen  contained  in  the  tritoxide  was 
disengaged,  and  escaped  in  the  gaseous  form. 

Jlfrs  B.  When,  without  the  presence  of  an  acid,  this  black  oxide  is  heated 
to  redness,  a  similar  change  takes  place.  Oxygen  gas  escapes  from  it,  and, 
instead  of  a  tritoxide,  it  becomes  a  deutoxide(27). 

But  we  must  hasten  to  some  other  general  properties  and  combinations 
of  the  metals.  Do  you  know  what  is  meant  by  an  alloy  ? 

Emily.  I  understand  by  an  alloy  something  which  debases  a  metal,  and 
renders  it  less  valuable. 

Jlfrs  B.  Your  idea  is  not  quite  correct.  Alloys  are  merely  combina- 
tions of  two  or  more  metals  with  each  other.  Gold  and  silver  are  alloyed 
with  copper,  when  they  are  to  be  made  into  coin,  or  into  articles  of  plate 
or  jewelry.  Standard  gold  and  silver  contain  about  one-twelfth  part  of 
alloy,  and  they  are  rendered  harder,  and  more  fit  for  use  by  this  mixture, 
Brass  is  an  alloy  of  copper  and  zinc;  beil-metal,  an  alloy  of  copper  and 
tin;  and  pewter,  of  tin,  with  lead,  antimony,  or  some  other  metal  or  metals; 
its  composition  being  various(  28). 

Emily.  I  am  a  little  at  a  loss  about  the  nature  of  tin.  Our  tin  dishes,  and 
cups,  and  kettles,  differ  very  much  from  a  pair  of  tea-pots  which  we  have 
in  uso,  and  which  are  warranted  to  be  pure  tin. 


23.  What  remark  does  Emily  make  on  the  solution  of  oxides  ? 

24.  Describe  the  manner  of  naming  the  metallic  oxides. 

25.  Which  oxide  of  a  metal  does  an  acid  generally  dissolve? 

26.  How  is  this  shown  by  the  black  oxide  of  manganese? 

27.  How  do  acids,  or  heat,  extricate  a  portion  of  its  oxygen? 

28.  What  are  alloys,  and  what  particular  examples  are  given? 


ON  MALLEABILITY  AND  DUCTILITY.  187 

Mrs  B.  What  we  call  tin,  or  tin  plates,  and  out  of  which  the  common 
tin  ware  is  made,  is  thin  sheet  iron  covered  with  tin,  just  as  the  inside  of 
copper  saucepans  is  covered  in  the  operation  called  tinning.  This 
coating  of  tin  is  applied  by  dipping  the  sheets  of  iron,  properly  prepared, 
into  melted  tin.  An  alloy  of  tin  and  iron  is  thus  formed  upon  the  surface,  to 
•which  a  thin  coat  of  pure  tin  adheres,  whilst  the  middle  is  sheet  iron. 

Caroline.  That  accounts  for  the  rusting;  (I  heg  your  pardon,  now  that  I 
am  a  chemist,  I  should  say  oxidizing)  of  the  vessels  when  they  have  been 
much  used;  the  tin  in  this  case  being  worn  off  from  the  surface  of  the 
iron. 

Mrs  B.  Pure  tin  is  a  very  soft  malleable  metal,  which,  if  made  thin, 
like  tin  ware,  would  bend  as  easily  as- paper(29). 

Emily.     By  malleable,  I  believe  you  mean  soft  and  flexible,  do  you  not? 

Mrs  B.  Not  precisely.  Some  metals  are  said  to  be  malleable  and 
ductile,  and  others  to  be  brittle.  Malleability  and  ductility,  though  both 
opposed  to  brittleness,  are  yet  different  from  each  other.  JBy  malleability 
Is  meant  the  capacity  of  being  beaten  out  into  very  thin  plates  or  leaves;  and 
ty  ductility,  a  capability  of  being  dra-wn  into  very  fine  Tvire(SQ). 

Caroline.  But  certainly  those  metals  which  can  be  beaten  into  thin 
leaves  may  also  be  drawn  into  fine  wire:  I  do  not,  therefore,  see  the  dis- 
tinction between  the  two. 

Mrs  B.  Nevertheless,  these  properties,  although  always  combined  to 
a  certain  degree,  are  absolutely  and  evidently  distinct.  Iron,  for  instance, 
can  be  drawn  into  wire  of  extreme  fineness,  yet  it  cannot  be  beaten  into 
very  thin  leaves;  and  other  examples,  equally  decisive,  might  be  given(3i). 

Caroline.  That  is  strange,  and  I  cannot  conceive  of  any  principle  upon 
•which  we  can  account  for  such  a  fact. 

Mrs  B.  I  can  only  tell  you  what  plausible  conjecture  has  been  made 
upon  this  point,  which,  if  admitted  to  be  true,  will  satisfactorily  account 
for  it.  It  has  been  supposed  that  the  minute  particles  of  the  most  ductile 
metals  are  in  the  form  of  fine  fibres  like  cotton,  whilst  those  of  the  malle- 
able metals  are  in  the  form  of  flat  plates  like  spangles(32).  The  former 
structure  would  evidently  t,e  best  adapted  to  the  formation  of  wire;  the 
latter  to  extension  into  thin  leaves.  Remember,  however,  that  this  ex- 
planation is  to  be  taken  as  conjecture  only,  although  it  derives  some  sup- 
port from  the  known  fibrous  texture  of  iron,  the  most  ductile  of  all  the 
metals.  We  must  now  return,  from  our  digression,  to  the  subject  of  alloys, 
respecting  which  I  have  something  further  to  say. 

Emily.  I  was  about  to  inquire  concerning  them;  whether  we  are  to  con- 
sider them  as  mere  mechanical  mixtures,  or  as  chemical  combinations  of 
the  metals? 

Mrs  B.  They  are,  undoubtedly,  chemical  compounds;  for,  although 
they  retain  their  general  characteristics  as  metals,  they  undergo  changes 
which  are  evidently  not  mechanical.  In  many  instances  the  alloy  has 
neither  the  colour,  specific  gravity,  tenacity,  or  fusibility,  which  would  have 
been  anticipated  from  a  knowledge  of  the  separate  metals.  Copper,  which 
is  red,  united  to  zinc,  which  is  white,  produces  brass,  which  is  yellow. 
Copper  and  tin,  which  are  both  malleable,  form  bell-metal,  which  is  ex- 
tremely brittle.  A  compound  of  five  parts  of  bismuth,  three  of  tin,  and 
two  of  lead,  is  called  the  fusible  alloy,  and  melts  at  the  heat  of  boiling 


29.  What  observations  are  made  respecting  tin? 

SO.  What  is  meant  by  malleability  and  by  ductilityl 

31.  What  proof  is  given  of  a  difference  in  these  properties? 

32.  Upon  what  circumstance  is  this  supposed  to  depend? 


188  CONVERSATIONS  ON  CHEMISTRY. 

water,  although  the  most  fusible  of  these  three  metals,  \vhenalone,  requires 
a  temperature  of  between  four  and  five  hundred  degrees  to  melt  it.  Were 
the  alloys  mere  mixtures  of  the  metals  composing  them,  they  ought,  -when 
fused,  to  separate  in  consequence  of  the  difference  of  their  specific 
gravities(33). 

Emily.  When  articles  of  metal  are  broken,  I  hear  sometimes  of  their 
being  soldered,  and  at  other  times  of  their  being  -welded.  What  is  the  dif- 
ference between  these  processes?  ».  ,, 

Mrs  B.  Soldering  is  the  uniting  of  two  pieces  of  metal  together  by 
another  metal  (generally  itself  an  alloy),  which  is  melted  upon,  and  runs 
in  between  the  parts  to  be  joined.  The  solder  must,  of  course,  be  more 
fusible  than  the  metal  to  be  soldered(34).  Two  pieces  of  iron  may  be  sol- 
dered, or  brazed,  as  it  is  called,  by  means  of  brass.  Silver  or  brass  may 
be  soldered  by  a  mixture  of  brass  and  silver,  called  silver  solder,  which 
fuses  much  more  readily  than  either  of  them  alone.  Lead,  or  tin,  is  sol- 
dered by  a  mixture  of  these  two  metals  themselves,  which,  as  in  the  case 
of  silver  solder,  melts  at  a  temperature  below  that  of  either  of  its  con- 
stituents. This  latter  mixture  is  called  soft  solder,  whilst  the  former  kinds 
are  denominated  hard  solders(35).  When  either  of  these  solders  is  ap- 
plied, the  metal  is  made  clean  and  bright,  and  with  the  solder  some  substance 
is  used  which  operates  like  the  fluxes  employed  in  fusing  the  metals; 
that  is,  they  keep  off  the  atmospheric  air,  and  thus  prevent  oxidation,  which 
would  defeat  the  process(36). 

Caroline.  I  think  that  I  understand  the  nature  of  welding,  as  I  nave  se- 
veral times  seen  it  performed.  The  two  pieces  of  metal  to  be  joined  are 
heated  very  highly,  then  placed  upon  each  other  and  struck  with  a  hammer, 
which  unites  them  perfectly.  When  I  have  seen  this  done  it  has,  however, 
always  been  with  iron. 

Mrs  B.  Your  description  is  very  good,  and  the  reason  why  you  have 
seen  no  other  metal  than  iron  welded,  is  because  it  is  the  only  one  that  can 
be  so  united,  excepting  platina,  which  does  not  often  pass  under  the  ham- 
mer of  the  common  smith(37). 

The  last  general  property  of  the  metals  which  I  shall  notice  is  their  com 
bustibility,  which   I  have   the  means  of  exhibiting  to  you  very  brilliantly. 
This  will  close  our  present  conversation,  and  at  our  next  meeting  we  shall 
examine  some  of  the  individual  metals. 

Emily.  We  have  been  anxiously  waiting  to  see  the  operations  performed 
by  the  OXY-HTDROGEU  or  COMPOUND  BLOWPIPE.  We  have  heard  the  ex- 
periments with  it  described  in  such  glowing  colours,  its  power  of  com- 
bustion and  fusion  so  highly  extolled,  and  the  light  which  is  emitted  in 
these  processes  represented  as  so  dazzling,  that  I  think  the  reality  must  dis- 
appoint the  anticipation. 

Mrs  B.  You  need  not  apprehend  disappointment  in  witnessing  the  effects 
of  this  instrument,  although  we  must  limit  ourselves  to  a  very  few  examples 
of  its  power.  Lavoisier  had  applied  oxygen  gas  in  a  similar  way,  but  the 
apparatus  before  you  is  not  only  more  powerful,  but  much  more  manageable 
than  that  used  by  him.  When  oxygen  is  employed  alone,  as  was  the  case  iu 
the  experiments  of  the  French  chemist,  the  article  to  be  operated  upon  must 
be  first  ignited,  and  then  placed  under  the  stream  of  oxygen;  whilst,  in  the 
compound  blowpipe,  the  burning  hydrogen  renders  all  this  unnecessary. 

Caroline.     Is  there  any  thing  peculiar  in  the  construction  of  the  tin  ves- 


33.  What  proves  that  alloys  are  chemical  combinations? 

34.  What  is  meant  by  soldering,  and  how  is  it  effected? 

35.  What  particular  exemplifications  are  given? 

36.  What  precaution  is  necessary  to  prevent  oxidation? 

37.  What  is  -welding,  and  what  metals  may  be  welded? 


ON  THE  COMBUSTION  OF  THE  METALS. 


189 


sels  in  which  you  have  the  gases  collected  ?  You  hare  several  times  used, 
but  never  particularly  described  them. 

Jlfrs  B.  These  vessels  which  are  called  air,  or  gas,  holders,  are  very 
convenient  for  collecting  the  gases  in  large  quantities,  and  are  much  em- 
ployed by  the  chemist. 

This  (fig.  1.)  is  an  air-holder,  made,  as  you  observe,  of  tin,  and  japanned 
to  keep  it  from  rusting.  Its  construction  is  very  simple.  It  has  three  open- 
ings; one  for  filling  it  with  water,  another  for  admitting  the  gas  which  is  to 
displace  the  water,  and  the  third  to  allow  the  gas  to  escape  Avhen  wanted.  I.t 
is  first  filled  with  water  through  the  funnel  attached  to  the  top,  the  spout  or 
opening  near  the  bottom  being  stopped  with  a  cork.  The  second  opening 
in  the  top  is  for  the  escape  of  the  gas,  and  this  may  be  opened  or  closed  as 
iequired(38). 

Emily.     Was  this  the  kind  of  instrument  employed  by  Lavoisier? 


Jiir  Holder. 
Fig.   I. 


Hare's  Oxy-hydrogen  Blowpipe. 
Fig.  2. 


I  [Fig.  1.  A,  Body  of  the  gas-holder.  B,  a  funnel  for  filling  it  with  water. 
C,  a  tube  which  extends  from  it  nearly  down  to  the  bottom  of  the  vessel, 
its  end  always  dipping  under  water.  D,  a  turn  cock  to  allow  of  the  es- 
cape of  the  gas  when  wanted.  E,  a  tube  opening  into  the  body  of  the 
vessel,  to  admit  a  tube,  or  retort,  for  filling  it  with  gas,  and  for  allowing 
the  water  to  escape  as  the  gas  ascends. 

When  filled  with  gas,  and  water  is  poured  into  the  funnel  B,  its  pressure 
will  force  the  gas  through  the  opening  at  D,  to  which  a  blowpipe,  blad- 
der, or  other  instrument,  may  be  attached. 

Fig.  2.  Consists  of  two  air  holders  constructed  exactly  like  the  foregoing. 
One  of  these  is  to  be  filled  with  oxygen,  the  other  with  hydrogen.  Two 
tubes,  one  connected  with  each,  have  a  common  opening  at  C.  In  these 
tubes  there  are  turn  eocks  to  regulate  the  discharge  of  the  two  gases.  At 
D  is  the  substance  to  be  acted  upon,  which  may  be  placed  upon  a  piece  of 
charcoal,  or  any  suitable  support.] 


38.  Describe  the  vessel  usually  called  a  gas-holder? 


190  CONVERSATIONS  ON  CHEMISTRY. 

Jlfrs  It.  Yes;  and  the  compound  blowpipe  which  I  use  is  composed  of 
two  such  air-holders,  one  filled  with  oxygen,  the  other  with  hydrogen.  There 
is  a  pipe  leading  from  each  of  these  which  terminates  in  a  single  opening, 
from  which  the  gases  may  issue  either  separately  or  unitedly,  and  in  such 
proportions  as  may  be  desired. 

The  metal  to  be  burnt  is  most  commonly  placed  upon  charcoal;  it  is  held 
under  the  jet,  or  opening,  when  a  stream  of  hydrogen  is  allowed  to  escape, 
which  stream  is  then  ignited.  The  metal  exposed  to  the  flame  will  soon 
become  red-hot,  and  when  this  has  taken  place  oxygen  is  made  to  flow  upon 
it,  from  the  other  receiver.  This  will  produce  a  heat  of  very  great  intensity, 
and  a  piece  of  cast  iron  exposed  to  it  will,  as  you  see,  burn  very  rapidly(39). 

Caroline.  What  a  volume  of  splendid  sparks !  You  seemed  during  the 
combustion  to  be  enveloped  in  fire.  How  much  more  brilliant  this  is  than 
the  burning  of  the  wire  in  the  jar  of  oxygen ^ 

Emily.  Did  you  observe  that  the  iron  actually  boiled  up,  like  heated  wa- 
ter. This  experiment  could  not  indeed  disappoint  the  expectations  of  any 
one(40). 

J\frs  B.  A  piece  of  steel  watch  spring  will  burn  in  much  the  same  man- 
ner. Copper  you  perceive  burns  with  a  beautiful  green  flame,  and  the  other 
metals  with  flames  differently  coloured,  and  with  different  degrees  of  bril- 
liancy, whilst  they  fly  off  in  the  state  of  oxides(4l). 

Emily.  Those  which  have  been  called  perfect  metals,  such  as  gold,  silver, 
and  platina,  as  they  are  not  oxidized  by  heat  and  air,  will  not  burn,  I  sup- 
pose, but  merely  become  ignited  and  fused. 

Mrs  £.  Such  is  the  intensity  of  the  heat,  that  every  metal  yields  to  its 
influence.  Platina  will  not  melt  in  any  of  those  furnaces  in  which  other 
metals  are  fused;  but  under  the  action  of  the  compound  blowpipe  it  is  not 
fused  merely,  but  rapidly  dissipated  in  vapour.  Gold  and  silver  likewise 
burn,  being  not  only  oxidized,  but  actually  vaporized(42). 

Articles-  which  had  resisted  every  previous  attempt  to  fuse  them,  such  as 
the  pure  earths,  have  been  subdued  by  this  instrument.  Incombustible  sub- 
stances cannot,  of  course,  be  burnt  by  it,  yet  the  light  which  they  emit  is  so 
Extremely  dazzling,  that  the  eye  can  scarcely  bear  it.  A  tobacco-pipe  stem, 
or  a  piece  of  lime,  answers  well  for  this  experiment.  The  compound  blow* 
pipe  has  not  served  the  purpose  of  showing  brilliant  experiments  merely, 
but  has  greatly  aided  the  chemist  in  his  researches(43). 

Caroline.  To  whom  are  we  indebted  for  this  elegant  and  efficient  mode 
of  obtaining  the  command  of  so  high  a  degree  of  temperature  ? 

•Mrs  B.  To  Dr  Robert  Hare  of  Philadelphia,  now  professor  of  chemis- 
try in  the  university  of  that  city,  who  published  an  account  of  it  in  the  year 
1802.  The  effects  produced  by  it  upon  various  substances  were  subse- 
quently more  fully  ascertained  by  himself,  and  by  Professor  Silliman  of 
Yale  college,  and  made  known  in  the  journals  both  of  this  country  and  of 
Europe(44).  It  is  much  to  be  regretted  that  attempts  were  made,  many 
years  afterwards,  by  an  English  chemist,  to  deprive  Dr  Hare  of  the  honour 
of  the  invention,  and  of  the  investigations  to  which  it  gave  rise. 

Caroline.  And  were  the  experiments  in  England  performed  with  an  in- 
strument exactly  like  that  which  you  have  employed? 


39.  Describe  the  compound  blowpipe  and  the  mode  of  using  it. 

40.  How  is  cast  iron  affected  when  exposed  to  its  action? 

41.  What  is  observed  respecting  some  other  metals? 

42.  How  are  gold,  silver,  and  platina  acted  upon? 

43.  What  is  said  of  the  fusion  and  ignition  of  different  substances? 

44.  Who  was  the  inventor  of  the  compound  blowpipe,  and  what  observa- 
tions are  made  respecting  it? 

*    1 


ON  THE  COMBUSTION  OF  THE   METALS. 


191 


Mrs  B.  That  used  by  me  is  not  precisely  in  the  form  of  those  employed  by 
DrHare,  but  the  principle  of  its  action  is  the  same.  In  the  English  instru- 
ment, the  two  gases  were  mixed  together  in  the  proportions  in  which  they 
combine  to  form  "water,  and  forced  by  a  condensing  syringe  into  a  strong 
copper  box  or  reservoir,  whence  they  issued  by  their  elasticity  when  a  vent 
was  opened  for  that  purpose.  This  is  the  instrument,  but  it  is  not  charged 
with  the  gases(45). 

Blowpipe  -with  condensed  Oxygen  and  Hydrogen  Gases. 


[A,  the  reservoir  for  the  condensed  gases.     B,  the  condensing  syringe.    C, 
the  bladder  for  supplying  oxygen  and  hydrogen.     D,  the  moveable  jet] 

Emily.  But  such  a  mixture  of  the  gases  is  extremely  explosive  ;  how  is 
ft,  then,  that  when  ignited,  the  apparatus  is  not-iblown  to  pieces? 

Mrs  B.  This  has  actually  and  repeatedly  happened,  to  the  imminent 
danger  of  the  operator.  When  the  gases  are  highly  condensed,  and  the  aper- 
ture very  small,  they  flow  out  so  rapidly  as  to  prevent  the  flame  from  pass- 
ing inwards,  but  the  danger  is  every  moment  increasing,  and  several  contri- 
vances have  been  made  to  obviate  it ;  but  though  lessened,  it  still  exists  to  a 
very  considerable  extent(46). 

Emily.  The  instrument  with  condensed  air  is  certainly  the  most  com- 
pact of  the  two,  but  if  this  is  considered  as  a  point  of  importance,  why  cannot 
the  two  gases  be  separately  condensed  in  different  vessels? 

Mrs  B.  This  has  been  proposed,  and  might  very  readily  be  effected  ;  but 
i  those  who  have  been  in  the  habit  of  using  the  instrument  as  employed  by  Dr 
|  Hare,  are  satisfied  that  the  effects  it  is  capable  of  producing,  are,  in  all  res- 
:  pects,  equal  to  those  obtained  by  the  condensation  of  the  gases,  whilst  it  is 
i  entirely  free  from  the  danger  of  explosion. 

Caroline.  You  appear,  Mrs  B.,  to  be  making  a  mixture  of  the  filings  of 
copper  and  of  sulphur :  are  these  to  be  submitted  to  the  action  of  the 
blowpipe? 

Mrs  B.     No;  but  before  closing  our  present  conversation,  I  am  about  to 
I  show  you  a  kind  of  combustion  which  takes  place   without  the  presence  of 
Dxygen,  or  of  either  of  those  agents  which  have  been  denominated   suppor- 
I  ters  of  combustion.  Most  of  the  metals,  you  are  aware,  will  combine  with  sul- 
j  phur,  and  become  converted  into  sulphurets.      To  produce  this  combination, 
i  it  is  in  general  sufficient  to  expose  the  sulphur  and  the  metal,  in  mixture, 
!  to  a  degree  of  heat  not  far  surpassing  that  which  is  required  to  fuse  the  for- 
mer substance.  '4? 


45.  What  modification  of  this  instrument  has  been  since  made? 

46.  What  objection  exists  to  the  blowpipe  in  this  form? 


192  CONVERSATIONS  OX  CHEMISTRY. 

The  temperature  necessary  to  produce  this  result  does  not  exceed  that 
of  three  hundred  degrees.  When  this  has  been  attained  hy  the  mixture,  the 
heat  will  suddenly  rise  to  that  of  ignition,  and  the  whole  mass  will  assume  a 
glowing  red  appearance(47). 

I  put  this  mixture  of  flowers  of  sulphur  and  copper  filings  into  a  common 
Florence  flask,  which  I  close  to  prevent  the  admission  of  air.  I  now  place 
the  flask  over  a  lamp  and  heat  it  slowly,  and  you  will  presently  see  that 
ignition  will  take  place,  with  all  those  appearances  which  we  indicate  by 
the  word  burning(48).  The  disengagement  of  heat,  in  this  case,  results 
merely  from  the  union  effected  between  two  combustibles,  no  other  sub- 
stance being  present.  The  compound  formed  is  still  capable  of  under- 
going combustion  by  the  agency  of  oxygen  gas,  which  would  convert  its 
sulphur  into  an  acid,  and  its  metal  into  an  oxide. 

Emily.  And  it  seems  closely  to  justify  the  remarks  formerly  made  upon 
the  subject  of  combustion,  and  to  prove  that  it  may  result  from  intense  chem- 
ical action,  without  those  aids  by  which  it  is  ordinarily  supported(49). 


CONVERSATION  XIX. 

ON  THE  PARTICULAR  METALS. 

Metals  known  to  the  Ancients.  '  Those  -which  have  been  discovered  since 
the  15 th  century.  Gold,  its  mines,  modes  of  gilding  -with,  and  its  general 
properties.  Platinum,  its  properties,  and  the  ignition  of  Spongy  Platinum 
by  Hydrogen.  Metals  contained  in  the  ore  of  Platinum.  Silver,  Nitrate, 
and  Fulminate  of  Silver,  and  other  Fulminates.  Cinnabar,  Mercury,  it& 
Uses  and  Properties.  Iron,  Cast  Iron,  Steel,  and  Plumbago.  Magnetic 
Property  of  Iron  and  other  Metals.  Copper,  its  Uses  and  Combinations. 
Lead,  its  Oxides,  and  other  Combinations.  Tin,  its  Alloys  and  properties. 
Zinc,  and  its  combinations.  Acidifiable  Metals.  Arsenic,  Chrome,  and 
Antimony;  their  properties  and  uses.  Medicines  and  Pigments  obtained 
from  Metals. 

Mrs  J3.  I  have  already  intimated  to  you  that  in  examining  the  metals 
individually,  I  should  call  your  attention  only  to  the  most  important  of  ; 
their  particular  properties.  To  do  more  than  this  would  not  be  found 
either  useful  or  agreeable,  and  to  do  less  would  be  to  neglect  some  inter- 
esting facts  respecting  a  class  of  bodies  which  occupies  a  very  conspicuous  sta- 
tion, whether  viewed  in  its  connexion  with  science  or  with  the  arts  of 
civilized  life. 

Caroline.     I  have  felt  a  much  higher  degree  of  interest  in  the  metals, 
than  I  had  thought  it  possible  for  them  to  excite,  and  am  therefore  pre- 
pared to  continue  the  subject  with  an  assurance  of  undiminished  satisfac-  \ 
tion. 

Mrs  B.     I  have  prepared  a  catalogue  of  the  known  metals,  and  wish 
you  each  to  take  a  copy  of  it.     I  have  not  included  those  metals  which  are  the.' 
bases  of  the  alkalies  and  of  the  earths,  as  they  have  been   separately  con- ; 
sidered.      This  list  is  made  out  chronologically,  containing  the  date  of  the 
discovery  of  all  the  various  metals,  excepting  the  seven  which  were  knowo 
at  a  period  antecedent  to  that  of  authentic  history. 


ON  GOLD. 


193 


Names  of 
the  metals 

Date  of  their 
discovery. 

Names  of 
the  metals. 

Date  of  their 
discovery. 

Names  of 
the  metals. 

Date  of  their 
discovery. 

Gold 

1    o 

Arsenic 

1733 

Titanium 

1791 

Silver 

1  J* 

Cobalt 

1733 

Chromium 

1797(2) 

Iron 

2  a 

Platinum 

1741 

Columbium 

1802 

Copper 

>«i(n 

Nickel 

1751 

Palladium 

1803 

Mercury 

i  M 

Manganese 

1774 

Rhodium 

1803 

Lead 

1 

Tungsten 

1781 

Iridium 

1803 

Tin 

J 

Tellurium 

1782 

Osmium 

1803 

Antimony 

5th  century 

Molybdenum 

1782 

Cerium 

1804 

Zinc 

1520 

Jranium 

1789 

Cadmium 

1818(3) 

Bismuth 

6th  century 

Emily.  There  is  one  thing  very  remarkable  in  this  list,  and  which  serves 
to  exemplify  the  rapid  progress  of  chemistry  within  a  few  years.  I  al- 
lude to  the  modern  date  of  the  discovery  of  so  many  of  the  metals(4). 

JWrs  B.  And  if  we  had  included  those  which  are  furnished  by  the  decom- 
position of  the  alkalies  arid  the  earths,  this  fact  would  have  been  rendered 
still  more  striking,  the  whole  of  them  having  been  recently  made  known. 
I  have  not  thought  it  best  to  give  you  a  systematic  classification  of  them 
according  to  any  relationship  which  they  bear  to  each  other  in  their  proper- 
ties. While  examining  them  we  shall  proceed  in  such  order  as  may  appear 
to  be  most  convenient,  beginning  with  Gold. 

GOLD  is  the  only  simple  metal  which  has  a  yellow  colour.  It  is  always 
found  in  the  metallic  state;  sometimes  nearly  pure,  at  others  considerably 
alloyed  with  silver  or  with  copper.  Although  nature  has  diffused  it  in 
every  country,  it  has  been  either  in  quantities  so  sparing,  or  in  situations 
whence  it  is  procured  with  such  great  labour,  as  to  make  it  the  most  costly 
of  those  metals  which  have  been  brought  into  general  use.  In  some  places 
it  is  obtained  by  washing  the  sand  of  rivers,  and  in  others  from  soils  in  which 
it  is  .contained  in  minute  particles.  Occasionally  it  is  found  in  veins  in  solid 
rocks,  whence  it  is  necessary  to  quarry  immense  portions  of  stone,  in  order 
to  obtain  the  produce  of  a  thin  stratum  of  gold.  Shafts  are  sometimes  sunk, 
in  the  manner  of  wells,  to  the  depth  of  many  hundred  feet,  down  which  the 
miners  descend  by  means  of  ropes,  and  labour  in  great  peril  from  falling 
stones,  accumulated  water,  foul  air,  and  other  causes.  Mines  of  gold  are 
wrought  in  every  quarter  of  the  world,  but  Mexico,  and  some  of  the  coun- 
tries of  South  America,  have  furnished  more  of  this  metal  than  all  the  other 
regions  of  the  globe  collectively (5). 

Caroline.  North  Carolina  has  lately  been  much  spoken  of  on  account  of 
its  gold  mines.  I  have  seen  several  specimens  said  to  have  been  brought 
from  thence. 

Mrs  B.  A  very  considerable  quantity  has  been  found  there.  It  is  diffused 
over  an  extensive  region,  not  only  in  that  state,  but  extending  into  Virginia, 
South  Carolina,  and  Georgia.  This  region  resembles  that  of  the  gold  dis- 
tricts of  Mexico.  Some  years  ago  there  was  a  piece  of  gold  found  in  North 
Carolina,  which  weighed  twenty-eight  pounds.  This  large  mass  I  saw  de- 


1.  What  are  the  seven  metals  which  were  known  to  the  ancients? 

2.  What  others  were  discovered  previously  to  the  year  1800? 

3.  Name  those  discovered  during  the  present  century. 

4.  What  particular  fact  does  the  table  of  the  metals  exemplify? 

5.  In  what  conditions  and  in  what  countries  is  gold  found? 

R 


194  CONVERSATIONS  ON  CHEMISTRY. 

posited  in  the  United  States  mint  in  Philadelphia.  Other  pieces  have  since 
been  found  weighing  several  pounds,  but  this  is  an  event  of  very  rare  occur- 
rence^). 

Caroline.  I  believe  that  gold  is  beaten  into  leaves  which  are  much  thin- 
ner than  those  of  any  other  metal. 

Mrs  B.  It  is  ;  and  such  is  its  malleability,  that  about  280,000  leaves  of 
gold  piled  upon  each  other,  will  measure  but  one  inch  in  thickness,  and  the 
gilding  upon  silver  wire  is  but  about  a  twelfth  part  of  the  thickness  of 
one  of  those  leaves;  yet  the  silver  will  be  found  completely  covered  and  hid- 
den by  the  gold,  even  when  the  wire  is  examined  by  a  microscope(Z). 

Emily.  A  perfect  coating  formed  by  a  layer  not  the  three  millionth  part 
of  an  inch  in  thickness!  How  extremely  minute  must  be  the  particles  of 
gold! 

•Mrs  B.  Gold  may  be  dissolved  in  a  mixed  acid,  which  has  been  called 
aqua  regia.  It  is  made  by  mixing  together  portions  of  nitric  and  muriatic 
acids.  Neither  of  these  alone  will  dissolve  the  metal,  but  they  do  so  very 
readily  when  combined.  I  put  a  leaf  of  gold  into  each  of  these  wine  glas- 
ses; upon  one  I  pour  nitric,  upon  the  other  muriatic  acid,  and  you  see  that 
ia  both,  the  leaf  remains  unchanged.  I  now  pour  the  two  together,  and  the 
gold  is  immediately  dissolved.  This  mixture  of  acids  is  now  usually  de- 
nominated nitro-muriatic  acid,  and  the  salt  of  gold  which  results  from  this 
combination,  nitro-muriate  ofgold(8). 

Caroline.  The  muriatic  acid,  I  recollect,  is  that  which,  with  ammonia, 
forms  sal  ammoniac,  or  the  muriate  of  ammonia. 

J\frs  B.  Gold,  from  its  beauty  and  durability,  is  employed  for  gilding  th< 
less  valuable  metals,  as  well  as  numerous  articles  made  of  wood,  and  other 
materials.  Gilding  is  effected  in  various  ways.  Sometimes  the  metal,  in  thin 
leaves,  is  made  to  adhere  by  means  of  size,  or  varnish;  at  others  the  gold  is 
dissolved  in  mercury,  and  in  this  combined  state  is  applied  to  silver,  copper, 
bronze,  or  other  metals  to  be  gilt(9). 

Caroline.  By  saying  that  the  gold  is  dissolved  in  mercury,  you  mean,  ] 
suppose,  that  an  alloy  of  these  two  metals  is  prepared  by  melting  them  to- 
gether. 

Mrs  B.  Mercury,  being  already  in  the  fluid  state,  will,  like  other  fluids, 
dissolve  those  solids  to  which  it  has  a  strong  attraction.  Gold  is  one  of  them, 
and  although  the  solvent  power  of  the  mercury  is  increased  by  heat,  it  wili 
operate  whilst  cold.  Silver,  copper,  and  in  fact  most  of  the  metals,  combine 
in  like  manner  with  quicksilver.  Compounds  of  this  kind  are  usually 
of  a  soft,  pasty  consistence,  and,  although  of  the  nature  of  alloys,  they  are 
classed  by  themselves  and  called  amalgams.  Thus  we  say  an  amalgam  of 
gold,  an  amalgam  of  tin,  &c.(10). 

When  the  amalgam  of  gold  is  used  for  gilding,  it  is  spread  over  the  sur- 
face of  the  metal  to  be  gilt,  which  must  therefore  be  of  a  kind  to  which  it 
has  an  affinity.  The  metal  so  covered  is  then  heated  over  a  charcoal  fire,  which 
volatilizes  the  mercury,  whilst  the  gold  is  left  adhering  to  the  surface  in- 
tended to  be  gilt.  This  operation  is  sometimes  called,  though  not  very 
appropriately,  water  gilding(ll). 

We  must  now  leave  the  consideration  of  gold,  and  proceed  to  that  of  a 
less  costly  metal. 


6.  What  is  remarked  respecting  gold  mines  in  the  United  States? 
T.  How  thin  may  gold  be  beaten,  or  be  spread  in  gilding? 

8.  In  what  acid  can  gold  be  dissolved? 

9.  By  what  methods  may  gold  be  applied  in  gilding? 

10.  To  what  combination  of  metals  is  the  term  amalgam  applied? 

11.  How  is  the  amalgam  of  gold  employed  in  gilding? 


ON  PLATINUM.  195 

Emily.  Let  me  first  try  if  I  can  repeat  the  principal  properties  of  gold. 
It  is  never  mineralized,  being  always  found  in  the  metallic  state.  It  may 
be  oxidized  by  electricity,  or  by  aqua  regia,  but  not  by  heat,  moisture  or  air, 
either  individually,  or  united;  and  it  is  one  of  those  metals,  the  oxides  of 
•which  may  be  reduced  by  heat  alone.  It  is  more  malleable  than  any  other 
metal,  is  the  only  one  of  a  yellow  colour,  brass  being  an  alloy;  and  with 
mercury  it  forms  an  amalgam(12).  Am  I  correct,  Mrs  B.  ? 

Mrs  B.  Perfectly  so;  and  we  will  now  examine  the  metal  to  which  I 
just  now  alluded;  it  is  PLATINA  or  PLATINUM. 

Caroline.  I  observe  that  you  frequently  give  the  names  of  the  new  metals 
with  a  termination  in  urn.  I  think  science  would  do  better  without  these 
double  names. 

J\frs  B.  Uniformity  has  been  attempted  in  this  as  well  as  in  most  of  the 
other  departments  of  chemistry.  Most  chemists  have  adopted  the  ter- 
mination in  urn,  in  naming  the  new  metals.  No  one,  however,  expects  the  long 
established  names  of  gold,  silver,  iron  and  copper,  to  be  changed  in  con- 
formity with  new  rules;  nor  shall  I  always  follow  them  in  our  conversar 
tions,  even  with  the  new  metals(13). 

Pure  platinum  is  of  a  white  colour,  somewhat  resembling  silver.  Like 
gold,  it  is  always  found  in  the  metallic  state,  and  usually  associated  with 
that  metal.  Formerly  it  was  obtained  only  from  the  mines  of  South  Ame- 
rica, but  latterly  it  has  been  discovered  in  considerable  quantities  in  the 
Uralian  Mountains,  and  the  Russians  have  actually  introduced  a  coinage  of 
this  metal(!4).  It  is  the  heaviest  body  known,  its  specific  gravity  being 
greater  than  that  of  gold;  and  it  is  so  infusible  as  to  retain  the  solid  state  in 
furnaces  the  most  intensely  heated.  It  may  be  melted,  however,  by  the  oxy  • 
hydrogen  blow-pipe,  in  the  current  of  a  powerful  voltaic  battery,  and  by  the 
heat  of  the  solar  ray  contracted  by  a  lens(15). 

Caroline.  If  platina  cannot  be  fused  in  a  furnace,  how  then  can  it  b« 
brought  into  large  masses  for  use  in  the  arts? 

.Mrs  B.  By  the  property  of  welding,  possessed  only  by  it  and  by  iron. 
Platina  is  soluble  in  the  same  acid  which  dissolves  gold,  but  in  no  other; 
and  on  account  of  the  little  effect  produced  upon  it  by  heat  and  most  of  the 
chemical  agents,  it  is  found  of  great  use  in  forming  some  of  the  vessels 
required' in  the  laboratory(lG). 

Emily.  What  is  the  use  of  that  neat  little  instrument  which  you  have 
taken  from  the  case?  Can  it  have  any  connexion  with  platinum? 

Jtfrs  B.  It  is  intended  to  exemplify  a  very  remarkable  property  in  this 
metal.  A  soft,  spongy  mass  of  platinum  may  be  obtained  by  dissolving  it 
in  nitro-muriatic  acid,  precipitating  it  from  its  solution  by  means  of  muriate 
of  ammonia,  and  then  igniting  the  precipitate  in  a  crucible.  It  is  no\r 
called  spongy  platinum.  If  a  stream  of  hydrogen  gas,  at  the  common 
temperature,  be  made  to  blow  upon  this  spongy  mass,  or  even  upon 
platinum  made  into  thin  leaves,  or  very  fine  wire,  and  rolled  up  so  as  to 
form  a  ball  about  the  size  of  a  pea,  the  metal  will  become  ignited,  and  will 
set  fire  to  the  gas.  This  little  air-holder  contains  hydrogen,  which  is  forced 
out  by  the  pressure  of  water,  as  in  the  larger  instruments.  When  I  turn 
the  key,  the  gas  from  the  jet  blowing  upon  the  little  ball  of  platina,  quickly 


12.  Give  a  recapitulation  of  the  general  properties  of  gold. 

13.  What  is  said  of  the  termination  in  urn  in  naming  the  metals? 

14.  What  is  the  appearance  of  platinum,  and  where  is  it  found? 

15.  What  is  said  respecting  its  infusibility  ? 

16.  How  are  separate  pieces  united  together,  and  what  acid  dissolves  it? 


196 


CONVERSATIONS  ON  CHEMISTRY. 


ignites  it.  This,  in  its  turn,  sets  fire  to  the  gas,  the  flame  of  which  lights  the 
taper  over  which  it  passes(17). 

Spongy  Platinum  Apparatus. 


[A.  Glass  vessel  containing  diluted  sulphuric 
acid,  and  within  which  is  suspended  a  cylin- 
der of  zinc,  upon  which  the  acid  acts  and 
generates  hydrogen.  This  gas  forces  the  liquid 
up  the  tube,  and  into  the  upper  vessel  B. 
When  the  jet  C  is  opened,  the  hydrogen  will 
pass  out,  and  coming  into  contact  with  the 
ball  of  spongy  platinum,  D,  will  ignite  it.  The 
gas  will  then  inflame,  and  light  the  taper  E.  ] 


Caroline.  Wonderful  indeed!  and  I  should  think  it  a  phenomenon  very 
difficult  to  account  for.  The  metal  must  remain  unchanged,  as  hydrogen  can- 
not produce  any  chemical  effect  upon  it. 

Mrs  B.  The  chemists  do  not  pretend  fully  to  explain  it.  There  appears, 
however,  to  be  a  very  strong  analogy  between  this  phenomenon  and  the  me- 
chanical absorption  of  the  gases  by  charcoal  (p.  154).  The  presence  of  the 
oxygen  of  the  atmosphere  is  necessary  to  the  success  of  the  experiment;  and 
it  seems  as  though  the  hydrogen  was  mechanically  condensed  by  the  spongy 
platinum,  and  thereby  enabled  to  combine  chemically  with  the  oxygen,  and 
thus  to  produce  heat  and  light(18). 

In  these  metallic  grains,  which  are  called  the  ore  of  platinum,  four 
metals  have  been  discovered,  and  named  PALLADIUM,  RHODIUM,  OSMIUM, 
and  IBIDIUM. 

They  have  been  found  in  but  small  quantities,  and  you  must  at  present 
be  satisfied  with  the  knowledge  of  their  existence  only.  If  you  wish  to  in- 
quire further  concerning  them,  any  modern  treatise  on  chemistry  will  enable 
you  to  satisfy  your  curiosity(19). 

Emily.  I  never  should  have  supposed  that  the  grains  of  platina  in  this 
phial  consisted  of  so  many  different  metals:  this  ore  seems  indeed  to  be  an 
alloy  of  alloys. 

Mrs  B.  Besides  platinum  and  the  four  metals  just  named,  some  of 
the  older  metals,  also,  are  contained  in  these  grains,  making  the  whole  number 
amount,  it  is  said,  to  ten  or  eleven. 

We  will  now  pass  on  to  the  metal  which  is  generally  esteemed  next  in 
beauty  to  gold;  that  is  Silver. 

SILVER,  is  most  commonly  found  in  the  metallic  state  alloyed  with  other 
metals,  but  it  is  also  mineralized  with  sulphur,  forming  a  sulphuret  of  sil- 
ver. •  In  malleability,  silver  is  inferior  to  gold  only;  it  is  also  more  sus- 
ceptible of  being  oxidized.  When  kept  intensely  heated  for  a  considerable 
length  of  time,  in  contact  with  oxygen,  it  absorbs  a  portion  of  it.  Its  oxide, 
however,  may  be  reduced  by  heat  alone(20). 

Caroline.  I  have  understood  that  the  substance  called  lunar  caustic, 
which  is  used  in  surgery,  is  a  preparation  of  silver.  If  so,  my  own  expe- 
rience has  taught  me  that  silver  is  not  always  productive  of  pleasure. 


17.  What  is  spongy  platinum,  and  how  is  it  employed  to  produce  igni- 
tion? 

18.  On  what  principle  is  this  supposed  to  be  effected? 

19.  Name  the  metals  discovered  in  the  ore  of  platinum. 

20.  What  are  the  first  observations  made  respecting  silver? 


ON  MERCURY.  197 

Mrs  B.  B  oth  the  lunar  caustic  and  the  permanent  marking  ink  are  nitrate* 
of  silver;  the  former  in  a  solid  state,  the  latter  in  solution.  Nitric  acid  very 
readily  dissolves  silver,  and  this  nitrate,  dried,  fused,  and  cast  into  moulds, 
forms  lunar  caustic,  which  rapidly  corrodes  the  flesh.  When  the  nitrate  of 
silver  is  used  as  a  marking  ink,  the  linen  is  first  moistened  with  a  solution 
of  carbonate  of  soda  or  some  other  alkali,  then  dried,  and  the  writing  exe- 
cuted with  the  nitrate  of  silver,  which  stains  the  linen  of  a  permanent  dark 
colour(2i). 

Emily.  I  have  heard  it  said  that  those  dangerous  playthings  called  torpe- 
does, which  explode  when  thrown  upon  the  floor,  derive  this  property  from 
some  preparation  of  silver.  Is  this  the  fact? 

JMrs  B.  There  are  several  metallic  preparations  which  are  extremely 
explosive;  particularly  those  of  gold,  mercury  and  silver.  That  used 
in  the  kind  of  crackers  to  which  you  allude,  is  called  detonating"  silver;  but 
there  is  a  similar  compound  called  fulminating  silver,  which  is  incom- 
parably more  violent  than  the  former.  It  is  considered  unsafe  to"  pre- 
pare more  than  a  single  grain  of  it  at  once.  After  it  is  made,  it  is  dangerons 
even  to  remove  the  vessel  in  which  it  is  contained,  as  the  slightest  agitation 
will  cause  it  to  explode.  Even  a  drop  of  water  being  allowed  to  fall  on  it 
will  produce  the  effect. 

Emily.  And  do  these  different  preparations  appear  to  owe  their  explo- 
sive property  to  one  common  cause? 

Mrs  B.  They  do.  There  is  a  peculiar  acid  called  fulminic  acid,  which 
is  formed  under  particular  circumstances  when  such  metals  are  present, 
and  which  combines  with  them,  producing  salts  denominated  fulminates. 
This  acid  is  a  compound  of  carbon,  nitrogen,  and  oxygen,  which  are  sepa- 
rated from  very  slight  causes,  and  suddenly  assume  the  gaseous  form(22). 

MERCURY  OR  QUICKSILVER. 

You  need  not  to  be  informed  what  article  is  to  be  our  next  subject  of 
inquiry,  although  the  phial  containing  it  is  without  a  label. 

Caroline.  No;  quicksilver  can  never  be  mistaken  for  any  other  metal:  its 
great  weight,  and  its  fluidity  in  the  coldest  weather,  are  too  characteristic  to 
allow  of  our  calling  it  by  a  wrong  name.  It  is  so  peculiar  a  substance  that 
every  one  seems  to  find  amusement  in  playing  with  it.  Is  it  found  in  this 
state  in  the  mines,  or  is  it  a  solid  mineral? 

Mrs  B.  Sometimes,  though  rarely,  it  is  found  fluid,  and  is  then  called 
virgin  quicksilver.  Its  ore  is  usually  a  sulphuret.  The  colour  called  cin- 
nabar is  a  sulphuret  of  mercury.  The  beautiful  red  paint,  vermilion,  is 
also  compounded  of  the  same  materials,  prepared  with  great  care  by  the 
manufacturing  chemist(23). 

Mercury  is  much  used  at  the  gold  mines,  as  it  amalgamates  readily  with 
gold,  and  collects  from  the  soil  those  fine  particles  which  could  not  be  ob- 
tained in  any  other  way.  In  many  silver  mines,  also,  the  metal  is  wholly 
collected  by  amalgamating  it  with  mercury(24). 

Emily.  In  what  way  is  the  quicksilver  fixed  upon  the  backs  of  looking 
glasses?  It  seems  remarkable,  that  although  it  is  a  fluid,  it  does  not  run 

off-  3  &J| 

Mrs  B.     The  silvering  of  looking  glasses  is  effected  by  an  amalgam  of 


21.  For  what  purposes  is  the  nitrate  of  silver  employed. 

22.  What  is  said  respecting  fulminating  silver  and  other  fulminates? 
-23.  What  is  the  nature  of  the  article  denominated  cinnabar? 

24.  For  what  purpose  is  quicksilver  used  in  gold  and  silver  mines? 
R  2 


198  CONVERSATIONS  ON  CHEMISTRY. 

tin,  and  consists  principally  of  the  latter  metal,  which  gives  to  it  the  requi- 
site solidity  (25). 

There  are  two  oxides,  and  several  salts  of  mercury.  The  protoxide  is 
of  a  black  colour,  and  the  peroxide  red;  the  latter  is  commonly  called 
red  precipitate. 

This  red  precipitate,  when  heated  to  ignition,  gives  out  its  oxygen,  and 
returns  to  the  state  of  metallic  mercury.  It  is  an  article  very  interesting 
in  the  history  of  chemical  discovery,  as  it  was  from  this  oxide  that  Dr  Priest- 
ley first  obtained  oxygen  gas(26). 

Caroline.  I  think  that  you  mentioned  the  freezing  of  mercury  by  the 
natural  cold  of  some  climates. 

Mrs  JB.  Yes,  I  did;  although  in  order  to  its  existing  in  the  solid  state 
it  requires  to  have  its  temperature  reduced  thirty-nine  degrees  below  the 
zero  of  Fahrenheit's  scale.  It  is  then  not  only  a  solid,  but  also  a  malleable 
metal.  In  Siberia,  and  some  other  countries,  this  degree  of  cold  not  unfre- 
quently  occurs;  but  in  this  climate,  so  low  a  temperature  can  be  produced  by 
artificial  means  only.  When  mercury  has  been  frozen,  a  curious  effect  is 
produced  by  throwing  a  lump  of  it  into  a  glass  of  water.  The  water  will 
immediately  become  solid  ice,  and  the  mercury  at  the  same  moment  will 
become  fluid. 

Caroline.  Such  an  appearance  is  certainly  very  striking,  but  the  cause  is, 
I  think,  quite  evident.  The  mercury  will  reduce  the  water  below  its  freezing 
point;  whilst  the  heat  which  the  water  gives  out  in  becoming  solid,  will 
raise  the  temperature  of  the  mercury  sufficiently  to  bring  this  metal  into  the 
fluid  state(27). 

Mrs  B.  The  first  metals  to  which  I  called  your  attention,  are  usually 
esteemed  the  most  valuable;  but  even  gold  and  silver  are,  like  every  thing 
else,  valuable  only  in  their  proper  places.  There  is  another  metal,  gene- 
rally accounted  very  inferior  to  these,  which,  were  utility  made  the  only  test 
of  worth,  would  rank  far  above  either  of  them. 

Emily.  IRON  is  certainly  the  most  useful  of  all  the  metals,  and  is  un- 
doubtedly the  one  to  which  you  allude. 

Jltrs  B.  And  this  metal,  so  essential  to  the  arts  of  life,  nature  has  dif- 
fused with  a  most  bountiful  hand.  Traces  of  it  are  found  in  almost  every 
soil,  and  in  each  of  the  kingdoms  of  nature  ;  and  every  country  has  its  mines, 
whence  iron  may  be  obtained  in  abundance. 

The  existence  of  pure,  native  iron  is  doubtful.  Masses  of  this  metal,  some 
of  which  weigh  several  tons,  have  been  discovered  in  various  places  ;  but  as 
they  are  not  generally  in  the  vicinity  of  iron  mines,  and  all  of  them  resem- 
ble the  meteoric  iron,  in  being  alloyed  with  nickel,  they  are(28)supposed 
to  have  fallen  from  the  higher  regions  of  the  atmosphere. 

Caroline.  After  the  evidence  of  the  fall  of  meteorolites,  containing  a 
large  portion  of  iron,  I  do  not  see  why  tons  may  not  fall  from  the  heavens, 
as  well  as  pounds.  My  faith,  therefore,  does  not  stagger  under  the  weight 
of  this  ponderous  supposition. 

Jlfrs  B.  Iron  is  less  malleable,  but  more  ductile,  than  either  gold  or  sil- 
ver. It  may  be  drawn  into  wire  finer  than  a  human  hair,  and  which  will  sup- 
port a  weight  considerably  greater  than  a  wire  of  the  same  size  formed  of 
any  other  metal.  Although  in  the  impure  form  of  cast  iron,  it  is  readily 
fused  and  poured  into  moulds,  yet,  when  in  its  pure  state,  iron  is  melted  with 
difficulty  (29). 


25.  Of  what  does  the  silvering  on  looking  glasses  consist? 
526.  What  observations  are  made  on  the  oxides  of  mercury? 

27.  Narrate  the  facts  mentioned  respecting  the  freezing  of  mercury. 

28.  Is  iron  generally  diffused,  and  is  it  ever  found  native? 

29.  What  is  said  respecting  the  ductility  and  fusibility  of  iron? 


ON  IRON,  STEEL,  &c.  199 

Emily.  It  seems  that  the  metals  in  a  state  of  mixture  always  fuse  more 
readily  than  when  pure.  With  what  is  cast  iron  alloyed? 

Mrs  B.  Cast  iron  does  not,  as  you  seem  to  suppose,  owe  its  fusibility 
to  the  presence  of  another  metal,  hut  to  that  of  a  very  different  hody ;  to 
carbon,  between  which  and  iron  there  is  a  strong  affinity (30). 

Caroline.  I  should  certainly  never  have  suspected  such  a  combination  as 
that;  but  it  is  not  surprising  that  iron  should  lose  its  tenacity,  by  combining 
with  so  fragile  an  article  as  charcoal. 

Mrs  B.  This  is  the  principal,  though  not  the  only  impurity  in  cast  iron; 
and  the  art  of  refining  it  consists  in  the  removal  of  these  foreign  matters. 
You  are  aware  that  iron  and  steel  are  essentially  alike,  are  you  not? 

Caroline.  I  have  supposed  that  steel  was  highly  refined  iron  ;  or  I 
ought  rather  to  confess  that  my  ideas  upon  this  subject  have  been  very  vague. 
I  plainly  perceive  that  my  supposed  familiarity  with  the  nature  of  certain 
bodies,  has  had  the  effect  of  preventing  those  inquiries  which  would  have 
made  my  knowledge  real,  instead  of  imaginary. 

Mrs  JB.  Steel,  like  cast  iron,  contains  a  portion  of  carbon,  and  is,  there- 
fore, a  carburet  of  iron.  But  in  this  state  the  iron  is  free  from  all  other  im- 
purities, and  the  quantity  of  carbon  which  is  combined  with  it,  is  but  small, 
although  all  the  peculiar  properties  of  the  steel  result  from  its  presence. 

Steel  is  prepared  by  taking  bars  of  fine  malleable  iron,  and  imbedding  them 
in  pulverized  charcoal,  in  a  kind  of  oven,  built  for  the  purpose.  This  oven 
is  closely  stopped  up  so  as  to  exclude  the  air  of  the  atmosphere  :  it  is  then 
surrounded  by  fire,  and  its  contents  brought  to  a  red  heat.  After  being  kept 
in  this  condition  for  three  or  four  days,  the  bars  will  be  found  to  have  ab- 
sorbed a  portion  of  the  carbon,  which  will  have  made  a  sensible  addition  to 
their  weight.  The  iron  has  now  become  steel;  and  if  one  of  the  bars  is 
heated  to  redness,  and  suddenly  cooled  by  plunging  it  into  cold  water,  it 
will  be  rendered  extremely  hard.  It  is  this  property  which  qualifies  steel 
for  being  made  into  knives,  scissors,  axes,  and  all  the  various  kinds  of  cut- 
ting instruments. 

The  process  by  which  iron  is  converted  into  steel  is  called  cementation(3l ). 

Caroline.  Had  not  the  effects  of  chemical  combination  been  rendered 
familiarto  us,  by  what  we  have  previously  learnt,  the  assertion  that  iron  is 
rendered  capable  of  becoming  extremely  hard,  of  bearing  a  fine  edge,  and 
receiving  a  beautiful  polish,  merely  by  its  combination  with  charcoal,  would 
have  appeared  incredible  ;  but  this  fact  seems  only  to  add  one  other  to  the 
list  of  evidences  which  prove  that  the  sensible  properties  of  chemical  com- 
pounds are  independent  of  those  of  their  constituents. 

Mrs  B.  Were  further  proof  of  this  general  truth  necessary,  there  is 
a  substance  composed  of  the  same  materials  with  steel,  which  might  aid  in 
establishing  it.  The  substance  to  which  I  allude  is  black  lead. 

Emily.  Guided  by  the  name  and  appearance  only,  I  have  always  sup- 
posed that  black  lead  was  some  compound  of  the  metal  from  which  its  name 
is  derived. 

Mrs  B.  Neither  the  name  nor  appearance  afford  any  correct  indica- 
tion of  its  nature,  as  it  does  not  contain  a  single  particle  of  lead,  but  con- 
sists of  carbon,  nearly  pure,  combined  with  four  or  five  per  cent,  of  iron. 
This,  therefore,  is  also  a  carburet  of  iron.  In  mineralogy  it  is  known  by 
the  names  of  plumbago  and  of  ffraphite(32}. 

With  one  of  tl\e  most  important  salts  of  iron,  the  sulphate,  you  have 


30.  To  what  does  cast  iron  owe  its  fusibility? 

31.  In  what  way  is  iron  converted   into  steel,  and  what  is   the  process 
called? 

32.  What  names  has  another  substance  which  is  a  carburet  of  iron? 


200  CONVERSATIONS  ON  CHEMISTRY. 

already  some  acquaintance  ;  the  others  I  shall  leave  you  to  study  at  your 
leisure.  The  property  of  welding,  which  belongs  to  this  metal,  enhances  its 
value  a  hundred  fold,  and  is  another  of  those  simple  provisions  of  nature 
which,  in  so  many  instances,  have  left  upon  her  works  the  impress  of  design 
and  benevolence. 

One  other  circumstance  respecting  iron  must  close  our  notice  of  this 
metal  ;  I  mean  its  property  of  being  attracted  by  the  magnet,  and  of  beiug 
itself  rendered  permanently  magnetic. 

Caroline.  But  does  not  this  power  reside  originally  in  the  mineral  called 
the  loadstone. 

Mrs  B.  The  natural  magnet,  or  loadstone,  is  an  ore  of  iron,  and  derives 
its  magnetism  entirely  from  the  presence  of  this  metal;  but  artificial  mag- 
nets, made  of  steel  are  more  powerful  than  any  of  those  supplied  by  nature. 
There  are  two  other  metals  that  are  capable  of  becoming  magnetic  :  these 
are  nickel  and  cobalt(33). 

COPPER,  to  which  we  will  now  attend,  is  perhaps  second  only  to  iron,  in 
usefulness. 

Native  copper  is  frequently  found.  In  the  neighbourhood  of  Lake  Superior, 
there  are  enormous  masses  of  it  so  perfectly  malleable,  that  it  can  be 
wrought  without  being  first  fused  and  refined.  Although  native  copper  is  by 
no  means  rare,  the  metal  is  usually  found  mineralized,  and  there  are  but  few 
which  exist  in  a  greater  variety  of  combinations  than  this.  Many  of  its  ores 
exhibit  beautiful  colours  ;  these  are  frequently,  though  not  by  any  means 
uniformly,  green  or  blue(34). 

Emily.  And  I  believe  most  of  its  salts  are  of  these  colours.  The  sulphate 
of  copper,  or  blue  vitriol,  and  the  nitrate  of  copper,  which  is  green,  you 
have  already  shown  to  us.  The  verdigris,  too,  that  forms  upon  our  copper 
saucepans,  is  always  of  one  or  other  of  these  colours(35). 

Mrs  B.  There  is  but  one  salt  of  copper,  properly  named  verdigris,  and 
this  consists  of  acetic  acid  (vinegar)  united  to  the  oxide  of  copper.  Every  salt 
of  copper  which  accidentally  forms  upon  the  utensils  employed  in  our  kitch- 
ens, is  called  verdigris,  but,  in  most  instances,  improperly(36). 

Caroline.  I  believe,  however,  that  there  is  one  general  truth  respecting 
them  all,  which  is  no  mistake,  and  that  is,  that  they  are  very  poisonous. 

Mrs  B.  In  giving  a  summary  of  the  properties  and  uses  of  copper,  it 
will  be  quite  safe  to  commence  with  your  observation.  Its  salts  are  all 
poisonous.  It  has  a  red  colour,  which  distinguishes  it  from  all  other  metals, 
excepting  titanium.  In  a  dry  atmosphere  it  undergoes  very  little  change  ; 
but  when  heated,  is  rapidly  oxidized.  It  forms  a  component  part  of  the  alloys 
called  brass,  bronze,  pinchbeck,  bell-metal,  and  several  others.  With  the 
exception  of  steel,  an  alloy  of  copper  and  tin  forms  the  best  cutting  instru- 
ments, and  was  used  for  this  purpose  by  the  ancients(37). 

You  may  now,  if  you  have  any  choice,  name  the  metal  to  which  we  shall 
next  attend. 

Emily.  LEAD,  it  seems  to  me,  may  claim  to    come   next  in  order,  if  we  \ 
give  a  preference  to  the  property  of  usefulness. 

Mrs  B.     I  think  your  remark  a  correct  one,  as  many  valuable  purposes 
are  answered,  not  only  by  the  pure  metal,  but  by  its  salts  and  alloys. 
1 

33.  What  is  said  of  the  magnetism  of  iron,  and  to  what  other  metals  may  ^ 
this  property  be  communicated? 

34.  What  is  said  of  native  copper,  and  of  its  ores  ? 

35.  What  are  the  usual  colours  of  the  salts  of  copper' 

36.  What  salt  of  copper  is  properly  called  verdigris  ? 

37.  What  are  the  general  properties  and  uses  of  this  metal? 


ON  LEAD,  TIN,  &c.  201 

Caroline.  I  believe  that  these  salts  may  be  classed  with  those  of  copper, 
being  very  poisonous. 

Mrs  B.  This  is  the  case  with  so  large  a  proportion  of  the  metallic  salts, 
that  excepting  in  individual  instances,  where  the  contrary  is  known,  it  is  most 
safe  to  treat  them  all  as  poisons(38). 

Most  of  the  lead  used,  is  extracted  from  an  ore  called  galena,  which  is  a 
sulphuret  of  lead.  Silver  is  very  frequently  found  combined  with  this  metal, 
and  when  its  quantity  amounts  to  four  or  five  per  cent,  it  is  worth  while  to 
^ extract  it,  but  not  otherwise(39). 

Caroline.    Red  lead,  you  informed  us,  is  an  oxide  of  this  metal. 

Mrs  B.  Yes.  There  are  three  oxides  of  lead;  the  protoxide,  commonly 
called  litharge,  the  deutoxide,  called  also  red  lead,  or  minium,  and  the  tritox- 
ide  or  peroxide,  which  is  of  a  deep  brown  colour,  and  is  frequently  called 
the  puce  coloured  oxide.  These  two  last,  when  heated,  give  out  oxygen,  and 
are  converted  into  the  protoxide,  or  litharge(40). 

Emily.  White  lead,  and  sugar  of  lead,  are  not,  it  seems,  among  the 
oxides;  I  suppose,  therefore,  that  they  are  salts  of  this  metal. 

Mrs  B.  You  are  correct;  -white  lead,  or  ceruse,  is  a  carbonate  of  lead, 
and  sugar  of  lead  is  the  acetate.  This  last  is  formed  by  boiling  either  litharge 
or  white  lead  in  vinegar(4l). 

Following  up  Emily's  idea  of  classing  the  metals  according  to  their  use- 
fulness, 1  think  that  tin  and  zinc  would  next  urge  their  claims,  and  perhaps 
with  equal  force.  Without  pretending  to  decide  between  them,  we  will  first 
take  some  notice  of  tin. 

I  have  already  told  you,  that  what  is  commonly  called  tin,  consists  of 
sheets  of  iron,  covered  with  that  metal. 

TIN  is  extremely  soft,  and  very  malleable.  It  is  beaten  into  leaves  called 
tin  foil,  and  may,  in  this  way,  be  reduced  to  the  one-thousandth  part  of  an 
inch  in  thickness,  which  is  by  no  means  the  limit  of  its  malleability.  When 
a  bar  of  tin  is  bent,  a  peculiar  crackling  noise  is  heard,  which  is  called  the 
cry  oftin(&}. 

Do  you  recollect  the  alloys  of  tin,  which  I  formerly  named  to  you? 

Caroline.  I  remember  two  ;  pewter,  which  is  usually  made  of  tin  and 
lead ;  and  bell-metal,  which  is  a  mixture  of  tin  and  copper. 

Mrs  B.  Petoter  varies  much  in  its  composition  ;  and  is  said  sometimes 
not  to  contain  any  lead.  Bell  metal  is  a  very  brittle  alloy,  although  both  the 
metals  of  which  it  is  composed  are  malleable. 

Gold  and  some  other  metals  are  also  rendered  extremely  brittle,  when 
alloyed  with  tin. 

Nearly  all  the  tin  used  in  the  world  is  obtained  from  Cornwall,  in  Eng- 
land, or  from  Malacca,  in  India.  It  is  the  most  fusible  of  all  the  metals  in 
common  use,  melting  at  about  440°  of  heat.  The  nitro-muriate  of  tin  is  used 
in  dying  red  morocco,  and  other  articles,  of  a  scarlet  colour.  The  muriate 
is  the  principal  salt  of  this  metal  used  in  the  arts(43). 

Emily.  The  next  metal,  ZINC,  is  not  now  new  to  us.  Its  use  in  the  ex- 
periments on  galvanism  has  made  us  familiar  with  its  appearance,  and  its 
employment  in  forming  with  copper  an  alloy  so  much  used  as  brass,  certainly 
gives  to  it  no  small  claim  to  consideration. 


38.  What  is  a  very  common  property  of  the  salts  of  the  metals? 

39.  What  ore  of  lead  is  the  most  abundant? 

40.  Give  the  chemical  and  common  names  of  the  oxides  of  lead? 

41.  What  is  white  lead,  and  what  the  sugar  of  lead? 

42.  What  are  the  distinguishing  properties  of  tin? 
4>3.   What  are  the  common  alloys  and  uses  of  tin.' 


202  CONVERSATIONS  ON  CHEMISTRY. 

Mrs  B.  In  commerce,  zinc  is  frequently  known  under  the  name  of  spelter. 
Calamine,  which  is  a  carbonate  of  zinc,  and  blende,  which  is  a  sulphuret, 
are  its  most  common  ores.  The  principal  uses  of  this  metal  have  been  already 
noticed,  and  need  not  to  be  repeated(44). 

Caroline.  You  sometimes  employed  it  in  preference  to  iron,  when  making 
hydrogen  gas,  and  I  then  observed  that  the  sulphate,  left  after  the  operation, 
crystallized  in  the  flask.  Is  thi  s  salt  of  any  use  ? 

Mrs  B.  The  sulphate  of  zinc  is,  in  commerce,  called  -white  vitriol.  It  is 
used  in  medicine,  and  in  the  arts  also,  though  principally  to  render  paint 
drying.  Nearly  all  the  acids  dissolve  zinc,  but  its  salts  are  generally 
unimportant(45). 

Caroline.  I  have  been  a  little  astonished  that  the  metals,  many  of  which 
combine  so  greedily  with  oxygen,  and  form  with  it  alkalies,  earths,  and 
oxides,  should  not,  like  the  other  simple  inflammables,  produce  acids  also. 

Mrs  B.  Then  you  will  not  be  surprised  to  learn,  that  there  are  several 
of  the  metals  which  do  actually  acquire  acid  properties  by  their  union  with 
oxygen.  Arsenic,  tellurium,  chrome,  molybdena,  tungsten  and  columbium, 
all  possess  this  character,  and  there  are  others,  which,  though  less  decidedly 
acidifiable,  have  yet  some  claim  to  admission  into  the  same  class(46).  The 
most  important  of  these  is  ARSENIC. 

Emily.  I  can  scarcely  hear  the  name  of  arsenic  without  feeling  some 
alarm,  it  is  so  deadly  a  poison,  and  accidents  with  it  have  been  so  frequent. 
I  had  no  idea,  however,  of  its  being  a  metallic  body. 

Mrs  B.  The  article  sold  in  the  shops  under  the  name  of  arsenic,  and 
sometimes  called  the  -white  oxide  of  arsenic,  is  arsenious  acid;  and  united 
with  a  larger  dose  of  oxygen,  it  becomes  arsenic  acid.  These  acids  combine 
•with  a  number  of  salifiable  bases,  forming  arsenites  and  arseniates(%7}. 

JLrsenic  is  sometimes  found  native,  but  more  commonly  in  combination 
with  other  metals.  It  is  volatile,  and  when  the  ores  which  contain  it  are 
heated  in  furnaces,  the  arsenic  is  sublimed,  combines  with  oxygen,  and  con- 
denses into  a  solid  mass  within  the  chimney,  whence  it  is  taken  in  thick 
cakes.  Metallic  arsenic  is  used  in  conjunction  with  copper  and  tin  in  mak- 
ing the  mirrors  for  reflecting  telescopes.  It  renders  their  texture  compact, 
their  colour  white,  and  makes  the  alloy  susceptible  of  a  finer  polish(48). 

Caroline.  What  is  sold  under  the  name  of  ratsbane  is  then  arsenious 
acid;  as  ratsbane  and  arsenic,  if  I  have  been  correctly  informed,  are  the 
same  thing. 

Mrs  B.  They  are  so.  But  this  article,  although  used  for  the  destruction 
of  vermin  on  account  of  its  poisonous  property,  has  formed  a  valuable 
medicine  in  the  hands  of  the  skilful  practitioner.  There  are,  indeed,  few 
physicians  who  have  not  employed  it. 

Another  of  these  metallic  acids  is  now  extensively  used  in  the  arts,  the 
base  of  which  is  called  chrome. 

CHROME  has  been  obtained  in  but  very  small  quantities,  as  its  reduction 
is  extremely  difficult.  It  is  usually  found  acidified  and  combined  with  iron. 
The  chromateofiron  exists  in  large  quantities  at  Unst  in  Scotland;  in  the 
United  States,  near  Baltimore  in  Maryland,  and  in  Chester  county,  Penn- 
sylvania. It  is  principally  used  for  the  manufacturing  of  that  beautiful 
colour  called  chromic  yellow,  which  is  a  chromate  of  lead.  A  distinguishing 


44.  What  are  the  ores  of  zinc,  and  what  are  its  principal  uses? 

45.  What  is  -white  vitriol,  and  for  what  purpose  is  it  employed? 

46.  Name  the  metals  which  may  be  converted  into  acids. 

47.  What  is  the  nature  of  the  arsenic  of  commerce? 

48.  How  is  arsenic  obtained,  and  what  are  its  uses? 


ON  ANTIMONY,  &c.  203 

characteristic  of  this  acid  is  its  property  of  communicating  vivid  colours  to 
the  metallic  oxides. 

Emily.  I  am  acquainted  with  only  one  of  its  colours,  and  if  it  furnishes 
any  others  of  equal  brilliancy  and  purity,  it  is  indeed  a  valuable  article. 
Among  all  the  yellows  which  I  have  used  in  my  painting,  there  is  not  one 
•which  I  think  equal  to  the  chromic  yellow  in  its  perfect  freedom  from  every 
other  tint(49). 

J\frs  B.  ANTIMONY  is  the  only  remaining  substance  which  is  much  used 
in  the  metallic  state.  The  article  sold  under  this  name  is  the  sulphuret 
of  antimony,  and  is  the  ore  from  which  the  metal  is  obtained.  To  the  metal 
itself  the  older  chemists  gave  the  name  of  regulus  of  antimony.  It  is 
sometimes  found  native,  hut  is  usually  obtained  from  the  sulphuret(50). 

Antimony  sometimes  enters  into  the  composition  of  pewter;  and  mixed 
•with  lead  and  bismuth  it  forms  the  metal  of  which  printing  types  are  made. 
It  is  from  antimony  that  type-metal  derives  the  requisite  hardness,  and  the 
property  of  taking  a  fine,  sharp  impression  in  the  mould.  Its  oxides  also 
are  emplpyed  for  communicating  a  yellow  colour  to  glass  and  to  pottery 
(51). 

Caroline.  And  some  of  its  salts,  I  know,  are  used  in  medicine.  The 
names  of  tartarized  antimony,  and  of  antimonial  wine,  plainly  indicate  that 
the  articles  to  which  they  are  given  are  antimonial  preparations. 

JMrs  B.  The  preparations  of  antimony,  and  of  some  other  metals  which 
were  introduced  into  medicine  by  the  alchemists,  supply  the  physician  with 
some  of  the  most  active  and  most  useful  of  his  antidotes  to  disease;  for 
although  many  of  them  are  strong  poisons,  it  is  to  this  very  circumstance 
that  we  are  indebted  for  their  power  to  counteract  disease,  when  adminis- 
tered by  the  hand  of  skill  and  experience(52). 

Emily.  The  oxides  and  salts  of  the  metals  appear  likewise  to  furnish 
the  greater  number  of  the  colours  used  in  painting.  I  had  no  idea  that  so 
many  of  them  were  metallic. 

Mrs  B.  I  have  mentioned  hut  a  very  small  proportionate  number  of  the 
metallic  pigments,  because  I  would  not  fatigue  you  with  a  mere  catalogue. 
For  the  same  reason  I  have  merely  named  some  of  the  metals,  as  they  are 
studies  for  the  closet  rather  than  subjects  for  our  conversations.  The  oxide 
of  manganese  is  much  used  in  the  process  of  bleaching;  a  fact  which  will  he 
more  particularly  noticed  when  we  treat  of  chlorine.  COBALT  furnishes  that 
beautiful  blue  colour  called  zajjfre,  oir  smalt,  used  for  making  blue  glass, 
colouring  pottery,  and  other  purposes.  The  pearl  white,  sometimes  em- 
ployed as  a  pigment  by  the  ladies,  is  an  oxide  of  bismuth,  the  metal  which 
you  may  recollect  enters  into  the  composition  of  what  is  called  the  fusible 
alloy,  melting  at  the  temperature  of  boiling  water(53). 


49.  What  is  chrome,  and  what  its  most  useful  preparation? 

50.  What  is  said  respecting  the  sulphuret  and  the  regulus  of  antimony? 

51.  To  what  use  is  antimony  applied  in  the  arts? 

52.  What  remarks  are  made  on  the  medical  use  of  metallic  preparations? 

53.  What  is  said  of  metallic  pigments  or  colours? 


,204  CONVERSATIONS  ON  CHEMISTRY. 


CONVERSATION   XX. 

ON  AFFINITY,  AND  THE  LAWS  WHICH  GOVERN  CHEMICAL 
COMBINATIONS. 

Action  of  the  Voltaic  Battery  upon  Alkaline  Salts.  Acids  passed  through 
Alkaline  Solutions,  -without  combination.  Nature  of  Chemical  Affinity* 
Laws  by  which  it  is  governed.  Double  Elective  Attraction.  Law  of  Definite 
Proportions.  Atomic  Theory.  Combination  of  Gases  by  Volumes.  Newton's 
Opinion  respecting  ultimate  Particles  or  Atoms.  Relative  -weight  of  Atoms. 
Comparison  of  the  absolute  and  relative  -weights.  Practical  advantages  of 
the  Law  of  Definite  Proportions. 

'  * '  »  ,     '       <* 

Mrs  JB.  You  are  aware,  young  ladies,  that  it  was  my  intention  to  resume 
the  subject  of  CHEMICAL  AFFINITY  at  some  convenient  period.  The  time  has 
now  arrived  when  I  think  it  may  he  done  with  great  advantage.  We 
have  examined  the  greater  numher  of  the  simple,  or  elementary  bodies,  and 
have  traced  them  into  many  of  their  combinations.  In  doing  this,  it  has  been 
necessary  to  notice,  incidentally,  some  of  the  principles  by  which  these  com- 
binations are  governed  5  but  you  are  now  sufficiently  familiar  with  the  most 
important  chemical  agents,  to  understand  those  more  recondite  laws,  the  ex- 
istence of  which  has  been  discovered  by  the  laborious  researches  of  the 
chemist. 

Caroline.  I  need  not  inform  you  that  I  am  much  pleased  with  inquiries 
of  this  description.  I  think,  how'ever,  that  my  too  ardent  zeal  for  specu- 
lation has  been,  to  a  considerable  extent,  corrected  by  the  kind  manner  in 
which  you  have  so  repeatedly  placed  me  in  the  wrong,  when  I  have 
endeavoured  to  form  theories,  instead  of  acquiring  a  knowledge  of  experi- 
mental truths. 

Mrs  B.  I  have  been  much  gratified,  my  dear  girl,  to  observe  your  gradual 
but  steady  approach  towards  a  just  estimate  of  the  value  of  facts,  and  a 
conviction  of  the  necessity  of  an  intimate  acquaintance  with  all  those  which 
have  been  discovered,  relating  to  any  subject,  before  an  attempt  is  made  to 
connect  any  of  them  together  by  a  theory. 

Emily.  I  am  very  glad,  Mrs  B.  to  observe  that  you  have  prepared  the 
voltaic  battery ,  and  are  about  to  exhibit  some  experiments  with  it.  Its  power 
of  decomposition  is  so  remarkable,  as  to  connect  it  very  intimately  with  the 
subject  of  chemical  affinity. 

Mrs  B.  You  ha-ve  witnessed  the  facility  with  which  the  elements  of  water 
are  separated  from  each  other,  by  the  attraction  of  its  opposite  poles,  and 
you  have  been  informed  of  other  decompositions,  still  more  remarkable, 
which  are  effected  by  the  same  means  ;  one  or  two  of  these  it  is  my  purpose 
to  exhibit  to  you. 

Caroline.  And  can  you  decompose  the  more  complex  substances  in  the 
same  way  in  which  you  decompose  water,  which  consists  of  two  elements 
only?  Can  you,  for  example,  separate  the  acid  from  the  alkali  in  a  salt,  by 
means  of  electricity  ? 

Mrs  JB.  Very  readily.  We  will  take  some  of  this  solution  of  sulphate 
of  soda,  (Glauber's  salt,)  and  subject  it  to  the  action  of  the  battery:  you  will 
find  that  the  alkali  will  be  attracted  by  the  negative,  and  the  acid  by  the 
positive  wire,  with  a  force  sufficient  to  separate  them  from  each  other(l). 


1.  How  will  the  voltaic  battery  affect  an  alkaline  salt? 


DECOMPOSING  POWER  OF  VOLTAIC  ELECTRICITY.       205 

By  the  arrangements  which  I  have  made,  we  can  collect  the  products  of  the 
decomposition  in  separate  vessels,  as  we  formerly  did  the  oxygen  and  hydro- 
gen, when  we  decomposed  water. 

Alkaline  Salt  decomposed  by  Electricity. 


I  have  two  cups,  into  one  of  which  [C]  I  have  poured  the  solution  of  Glau- 
ber's salt;  into  this  likewise  dips  the  platina  wire  [N]  from  the  negative 
pole  of  the  battery.  The  other  cup  [B]  contains  water,  and  is  connected 
with  the  positive  pole,  by  the  opposite  wire  [P],  A  piece  of  moistened  cotton 
wick  forms  a  conducting  communication  between  the  two  cups.  The 
attraction  of  the  positive  pole  for  the  acid,  will  cause  it  to  leave  the  first  cup 
[C],  and  pass  along  the  cotton  wick,  into  the  water  of  the  second  cup  [B], 
where  it  will  be  found  in  solution;  whilst  the  alkali  will  be  detained  in  the  first 
cup  [C],  by  the  attraction  of  the  negative  pole  for  that  substance.  This  cup, 
therefore,  will,  at  the  conclusion  of  the  experiment,  contain  a  solution  of 
pure  soda.  I  have  had  the  experiment  in  progress  a  sufficient  length  of  time 
to  effect  the  object(2). 

Emily.  That  does,  indeed,  manifest  the  astonishing  power  of  electric 
attraction  in  overcoming  chemical  affinity.  Observe,  the  blue  vegetable 
infusion  which  you  have  dropped  into  one  of  the  cups  has  become  red,  and 
that  in  the  other  green;  showing,  in  the  first,  the  presence  of  an  acid,  and  in 
the  second,  that  of  an  alkali. 

Caroline.  But  what  would  have  been  the  result,  if  each  cup  had  been  filled 
with  the  saline  solution? 

Jlfrs  B.  Just  the  same  as  at  present.  The  acid  of  the  first  cup  [C] 
would  have  passed  into  the  second  cup  [B],  and  the  alkali  from  that  into  the 
first  cup  [C].  All  the  sulphuric  acid,  therefore,  would  have  been  found  in  one 
cup,  and  all  the  soda  in  the  other. 

Caroline.  Astonishing !  They  must  then  have  actually  passed  each  other 
in  going  along  the  cotton  into  their  respective  cups(3). 

Jin  Acid  passed  through  an  Alkaline  Solution. 
p -w       c^      A       c }    Q N 


Mrs  B.  We  can  vary  the  experiment  so  as  to  render  it  still  more  striking, 
by  using  three  cups,  and  putting  into  the  central  cup  [A]  an  alkaline  solution; 
the  Glauber's  salt  being  placed  in  the  negative  cup  (G),  and  the  positive 
cup  ( W)  containing  water  only.  The  acid  will  be  attracted  by  the  positive 
wire  (P),  and  will  actually  appear  in  the  vessel  (W),  after  having  passed 
through  the  alkaline  solution  contained  in  the  centre  cup  (A),  without  com- 


2.  Describe  the  manner  of  conducting  the  experiment? 

3.  If  each  cup  contained  the  salt,  what  would  be  the  result? 

S 


206  CONVERSATIONS  ON  CHEMISTRY. 

bining  with  it;  although,  you  know,  acids  and  alkalies  are  so  much  disposed 
to  unite (4). 

Emily.  It  is  no  longer  surprising  to  me,  that  the  discovery  of  voltaic 
electricity  should  have  greatly  advanced  the  inquiries  of  the  chemist  into 
the  composition  of  bodies,  as  the  power  of  your  apparatus,  which  you  say  is 
a  comparatively  small  one,  appears  to  be  superior  to  that  of  chemical  affinity, 
and  sufficient  to  counteract  the  energetic  attraction  which  subsists  between 
sulphuric  acid  and  the  alkalies.  What  then  may  not  be  expected  from  those 
magnificent  batteries  of  which  we  have  heard  you  speak(5). 

Mrs  B.  We  must  now  examine  those  laws  of  combination  which  are  to 
form  the  main  subject  of  our  inquiries  to-day.  Your  attention  has  beeii  so 
frequently  called  to  the  effects  of  chemical  attraction,  or  affinity,  that  you 
cannot  have  forgotten  what  are  the  circumstances  under  which  it  is  exerted, 
as  formerly  explained  to  you. 

Emily.  Certainly  not;  CHEMICAL  ATTRACTION  is  that  attraction  which 
subsists  between  bodies  dissimilar  in  their  natures,  and  which  occasions  them, 
to  combine  and  form  a  compound  possessed  of  properties  different  from  those 
of  the  combining  substances(6). 

J\Irs  B.  Very  well;  your  definition  comprehends  what  is  sometimes 
culled  the  first  law  of  chemical  attraction,  namely,  that  it  takes  place  only 
between  bodies  of  a  different  nature(7). 

Caroline.  That  we  understand,  of  course;  for  the  attraction  exerted  be- 
tween particles  of  a  similar  nature  is  the  attraction  of  aggregation  or  cohe- 
sion, and  is  independent  of  any  chemical  power. 

JMrs  B.  Another  law  of  chemical  attraction  is,  that  it  is  exerted  only  be- 
tween the  most  minute  particles  of  bodies;  and  hence  it  follows  that  mechani- 
cal division  promotes  chemical  action. 

Caroline.  That  is  a  circumstance  which  we  might  have  inferred;  for  it 
is  evident  that  the  more  fine  we  make  the  particles  of  different  substances, 
the  more  easily  and  perfectly  they  will  come  into  contact  with  each  other, 
which,  of  course,  must  greatly  facilitate  their  union.  Indeed,  we  habitually 
practise  upon  this  rule,  as  we  always  pulverize  a  solid  when  we  wish  to  dis- 
solve it  rapidly  in  a  fluid(8). 

•Mrs  B.  It  is  for  this  same  reason  that  bodies  act  most  readily  upon  each 
other  -when  one  of  them  is  in  a  state  of  solution.  It  was,  in  fact,  formerly 
laid  down  as  a  law,  that  bodies  would  not  act  chemically  upon  each  other 
unless  this  was  the  case.  There  are,  however,  many  instances  known  in  which 
new  combinations  may  be  formed  by  the  mutual  reaction  of  substances  which 
are  in  a  solid  and  perfectly  dry  state(9).  To  produce  this  effect,  such  sub- 
stances should  be  reduced  to  fine  powder,  and  mechanical  force  employed 
to  cause  the  particles  to  approximate. 

Observe;  I  rub  together,  in  this  mortar,  some  muriate  of  ammonia  and 
quicklime,  both  of  them  being  quite  dry.  When  separate,  neither  of  these 
substances  possesses  odour;  you  may  now  find  that  the  latter  character  is 
not  retained  by  them. 

Emily.  What  a  powerful  smell  of  ammonia,  and  so  acrid  it  actually  - 
makes  the  tears  run  from  my  eyes.  This  is  the  same  mixture  by  which  you  ' 
formerly  obtained  ammonia;  and,  of  course,  a  muriate  of  lime  is  now  formed  . 
by  the  union  of  the  acid  of  the  sal  ammoniac  with  the  lime(10). 


4.  Describe  the  experiment  as  performed  with  three  cups. 

5.  What  is  remarked  respecting  the  power  of  electrical  attraction? 

6.  What  is  affinity,- and  between  what  bodies  is  it  exerted? 

7.  What  is  the  first  law  of  chemical  attraction* 

8.  What  is  the  next  law,  and  what  is  said  respecting  it? 

9.  What  is  observed  respecting  the  effect  of  solution? 

10.  What  experiment  with  sal  ammoniac  and  quicklime  is  mentioned? 


ON  THE  LAWS  OF  CHEMICAL  AFFINITY.  207 

Mrs  B.  There  are  also  many  explosive  powders  which  ignite  by  a  very 
slight  friction,  and  which  might,  therefore,  be  fairly  presented  as  exceptions 
to  the  rule  advanced  by  the  older  chemists(ll). 

Another  law  of  chemical  attraction  is,  that  combination  may  take  place 
between  two,  three,  four,  or  even  a  greater  number  of  substances.  This  la\v 
you  have  seen  fully  exemplified  in  the  formation  of  several  saline  bodies,  as 
well  as  in  other  instances;  and  indeed,  I  am  sure  that  as  these  laws  are 
presented  to  you,  you  will  observe  that  I  am  only  bringing  together  rules 
with  which  you  have  already  some  acquaintance.  I  have  been  careful  to 
notice  most  of  them,  whenever  they  were  experimentally  illustrated(12). 

Emily.  And  I  am  sure  that  we  shall  derive  great  benefit  from  a  syste- 
matic repetition  of  these  laws  which  have  hitherto  been  presented  to  us  as 
isolated  facts. 

Mrs  B.  That  a  change  of  temperature  always  takes  place,  at  the  moment 
of  combination  is  a  very  important  law,  and  one  of  which  your  recollection 
will  readily  furnish  many  examples(13). 

Caroline.  The  simple  fact,  that  a  change  of  capacity  for  caloric  occurs 
whenever  bodies  combine  chemically,  must,  of  necessity,  render  this  law 
universal.  There  is  so  generally  a  change  of  form,  too,  when  bodies  com- 
bine, that  this  circumstance  alone  would  account  for  a  change  of  tempera- 
ture(14). 

Mrs  B.  Recollect,  however,  that  a  change  of  form  is  not  necessary  to  a 
change  of  temperature.  When  I  poured  cold  sulphuric  acid  and  water  to- 
gether, the  mixture  remained  fluid,  yet  the  temperature  was  raised  to 
upwards  of  three  hundred  degrees,  which  is  far  above  that  of  boiling  water; 
but  although  the  form  remained  unchanged,  the  mixed  liquids  were  more 
dense  than  in  their  separate  state,  and  their  capacity  for  caloric  was  conse- 
quently decreased(lS). 

I  will  here  repeat  another  law,  although  it  is  included  in  Emily's  defini- 
tion of  chemical  attraction;  it  is  this:  the  properties -which  characterize  bodies 
•when  separate,  are  modi/led,  or  completely  changed,  by  their  combination. 

Emily.  The  evidences  of  that  law  meet  us  every  where.  What  can  dif- 
fer more  completely  than  water  does  from  oxygen  and  hydrogen  gases;  or 
what  can  resemble  sulphur,  oxygen,  and  iron  less  than  does  common  cop- 
peras, the  sulphate  of  iron(16). 

Mrs  B.  The  law  that  a  body  possessing  an  attraction  towards  a  number 
of  others,  possesses  it  in  different  degrees,  was  explained  to  you  in  our  first 
conversation,  (p.  22,)  and  you  cannot  have  forgotten  the  tables  of  simple 
affinity  which  the  chemist  constructs  to  exhibit  this  fact.  The  principle 
upon  which  these  tables  depend  is  expressed  in  the  law,  that  the  force  of  che- 
mical affinity  between  the  constituents  of  a  body  is  estimated  by  that  which  is 
required  for  their  separation(lT). 

Caroline.  I  should  find  it  difficult  to  conceive  how  there  could,  in  fact, 
be  any  other  measure  of  this  force;  and  certainly  the  decompositions  which 
the  chemist  effects  must  depend  upon  his  knowledge  of  this  difference  in  the 
force  with  which  bodies  attract  each  other.  The  tables  of  simple  affinity 
must  be  a  most  perfect  guide  to  him  in  effecting  his  operations(lS). 


11.  What  other  compounds  illustrate  the  same  fact? 

12.  What  is  said  on  the  combining  together  of  several  different  bodies? 

13.  What  is  the  law  respecting  a  change  of  temperature  ? 

14.  What  are  the  observations  made  on  this  point? 

15.  What  remarks  are  made  respecting  sulphuric  acid  and  water? 

16.  What  is  the  law  relating  to  a  change  in  the  properties  of  bodies? 

17.  What  respecting  the  affinity  of  a  body  for  several  others.' 

18.  What  are  Caroline's  observations  regarding  this  law? 


203  CONVERSATIONS  ON  CHEMISTRY. 


Mrs  B.  You  estimate  the  utility  of  these  tables  too  highly.  Whenever 
the  decomposition  of  a  body  can  be  effected  by  the  addition  of  a  single  new 
substance,  the  change  is  said  to  take  place  by  simple  affinity,  and  then  such 
tables  are  very  useful;  but  it  often  happens  that  no  single  substance  will 
decompose  that  upon  which  the  chemist  wishes  to  operate,  and  he  finds  it 
necessary  to  add  to  it  another  compound  body,  in  order,  to  effect  his  pur- 
pose. In  this  case,  both  the  compounds  will  be  decomposed  by  the  mutual 
interchange  of  their  constituents,  and  two  new  compounds  will  be  formed. 
All  instances  of  this  kind  are  said  to  result  from  DOUBLE  ELECTIVE  ATTRAC- 
TION, or  complex  affinity (\.§). 

Emily.  Was  not  the  decomposition  of  water  by  phosphuret  of  lime,  a 
case  of  this  kind?  (p.  145.)  Both  the  water  and  the  phosphuret  of  lime  were 
decomposed,  whilst  phosphuretted  hydrogen,  and  phosphate  of  lime  were 
produced. 

Mrs  B.  This  was  an  instance  of  the  exertion  of  complex  affinity;  but  my 
present  object  will  be  best  attained  by  an  example  of  the  mutual  decomposi- 
tion of  two  salts.  This  you  will  easily  comprehend  by  the  assistance  of  a 
diagram,  or  table,  which  will  very  distinctly  present  an  example  of  double 
elective  attraction,  together  with  some  collateral  circumstances  accompanying 
the  decompositions  effected  by  it. 

These  diagrams  are  variously  constructed,  but  after  understanding  one  of 
them,  you  will  find  no  difficulty  with  others,  Although  they  may  be  differ- 
ently arranged. 

The  two  compounds  which  I  have  chosen  for  an  example,  are  the  sulphate 
of  soda,  (Glauber's  salt),  and  muriate  of  lime,  a  salt  which,  as  its  name  in- 
dicates, is  composed  of  lime  and  muriatic  acid.  If  these  two  be  mixed 
together  in  a  state  of  solution,  they  will  both  be  decomposed.  The  bases 
will  exchange  acids,  or,  if  you  please,  the  acids  will  exchange  bases,  and  two 
new  salts  will  be  formed.  This  is  the  table(20). 

..    ;,:'}.    , .,  .;  ~.^~   '.-'...'.-  / 

Muriate  of  Soda. 

A* 


SULPHATE  C        Soda          Muriatic  acid  ^  MURIATE 

OP  -\          and  and 

SODA.  LSulphuricacid.     Lime. 


v 

Sulphate  of  Lime. 

Caroline.  I  seem,  from  the  mere  view  of  your  diagram,  to  have  acquired 
some  insight  into  the  plan  of  such  tables,  although  I  am  not  quite  vain 
enough  to  attempt  an  explanation  of  it,  and  of  the  attractions  which  it  is  meant 
to  exemplify. 

Mrs  B.  On  the  outside  of  the  vertical  brackets  you  have  the  names  of 
the  original  salts,  and  on  the  inside  the  name  of  the  acid  and  base  composing 
each  of  them.  Above  and  below  are  the  new  compounds  produced  by  their 
decomposition.  The  soda  unites  with  the  muriatic  acid,  and  forms  mu- 
riate of  soda  (common  salt);  and  the  lime  with  the  sulphuric  acid,  producing 
sulph&te  of  lime  (plaster  of  Paris)(21). 

Emily.  This  diagram  certainly  renders  the  double  decomposition  ofthese 
salts  quite  clear;  and  it  is  plain  that  if  one  of  them  is  decomposed,  the  other 


19.  What  remarks  are  made  on  double  elective  attraction? 

20.  What  are  the  substances  chosen  to  exemplify  such  attractions? 

21.  Describe  the  table  for  exemplifying  complex  affinity. 


ON  COMBINATION  IN  DEFINITE  PROPORTIONS.  209 

must  be  so  also.  But  is  there  any  pai-ticular  reason  for  placing  the  muriate 
of  soda  above,  and  the  sulphate  of  lime  below? 

Mrs  B.  Yes,  a  very  sufficient  one.  Before  mixture,  both  salts  were  in 
solution;  but  their  decomposition  has  produced  one  soluble  salt,  the  muriate 
of  soda,  and  one  which  is  insoluble,  the  sulphate  of  lime.  The  solubility  of 
the  former  is  intended  to  be  shown  by  its  being  placed  above,  with  the 
bracket  pointing  upwards.  The  precipitation  of  the  latter  is  indicated  by 
its  being  placed  below,  with  the  bracket  pointing  downwards(22). 

Caroline.  If  lime  alone  had  been  added  to  the  sulphate  of  soda,  would 
not  a  sulphate  of  lime  have  been  formed?  Or  if,  instead  of  that,  muriatic 
acid  had  been  added,  would  not  a  muriate  of  soda  have  been  produced  by 
simple  affinity? 

JMrs  B.  The  sulphate  of  soda  would,  in  either  case,  have  remained  unde- 
composed;  as  neither  the  attraction  of  sulphuric  acid  for  lime,  or  of  muriatic 
acid  for  soda,  would  have  equalled  that  existing  between  sulphuric  acid  and 
soda.  But  when  the  two  operate  together,  the  decomposition  is  effected(23),. 

Emily.  This  seems  a  little  like  the  adhesion  of  two  articles  which  have 
been  cemented  together  too  firmly  for  the  strength  of  one  man  to  separate 
them,  but  which  might  be  drawn  asunder  by  the  power  of  two  men;  when 
each  of  them  would  obtain  a  share  of  the  spoil(24). 

Caroline.  There  is  a  circumstance  in  chemical  combinations,  respecting 
which  I  have  repeatedly  thought  of  making  an  inquiry.  The  same  bodies 
unite  in  different  proportions;  as,  for  example,  oxygen  and  the  metals.  We 
may  have  a  protoxide,  a  dentoxide,  and  a  tritoxide,  but  we  hear  nothing  of 
the  intermediate  states.  Yet,  if  it  requires  a  certain  quantity  of  oxygen  to 
form  a  protoxide,  and  double  this  quantity  to  produce  a  deutoxide,  there 
must  be  a  period  when  the  metal  is  passing  from  one  state  to  the  other,  and 
in  which  it  must  be  halfway  between  them(25). 

JMrs  B.  The  solution  of  this  difficulty  will  lead  us  to  the  discussion  of 
some  points,  which,  although  intricate,  are  yet  of  too  much  importance  to  be 
allowed  to  pass  unnoticed.  You  must  acquire  some  clear  ideas  respecting 
what  is  called  the  law  of  combination  in  definite  proportions,  and  the  atomic 
theory  of  the  chemical  constitution  of  bodies.  These  two  subjects  are  inti- 
mately connected  with  each  other,  and  are  necessary  to  the  understanding 
of  the  phenomena  of  chemical  attraction(26). 

There  are  some  bodies  which  combine  in  all  proportions;  as  alcohol  and 
water,  or  sulphuric  acid  and  water.  One  drop  of  the  acid  or  of  the  alcohol 
will  diffuse  itself  through  a  gallon  of  water,  or  one  drop  of  water  through  a 
gallon  of  either  of  them.  But  in  this,  as  in  all  such  cases,  the  substances 
are  united  by  a  very  feeble  attraction,  and  the  properties  which  characterized 
them  when  separate,  undergo  but  little  change  by  their  union;  resembling 
in  this  particular  a  state  of  simple  mixture(27). 

The  law  of  COMBINATION  IN  DEFINITE  PROPORTIONS  applies  to  every  case 
of  energetic  chemical  attraction;  that  is,  to  all  cases  in  which  the  properties 
of  bodies  are  considerably  altered  by  combination.  The  law  is  this;  a  com- 
pound substance,  so  long1  as  it  retains  its  characteristic  properties,  must  always 
consist  of  the  same  elements  united  together  in  the  same  proportions^]. 

JEmily.  I  think  that  this  truth  is  almost  self-evident.  For,  if  it  requires 
a  certain  quantity  of  an  alkali  to  neutralize  a  given  quantity  of  an  acid,  the 


22.  How  may  it  indicate  the  solubility  or  insolubility  of  a  salt? 

23.  Why  would  not  lime  alone  decompose  the  sulphate  of  soda? 

24.  What  simile  is  used  to  illustrate  such  double  decompositions? 

25.  What  inquiry  is  made  respecting  the  formation  of  oxides? 

26.  What  law  and  theory  are  involved  in  the  reply  to  this  inquiry? 

27.  What  is  said  of  bodies  uniting  in  all  proportions? 

28.  How  is  the  law  of  combination  in  definite  proportions  announced  ? 

S  2 


210  CONVERSATIONS  ON  CHEMISTRY. 

combination  of  a  greater  or  a  smaller  proportion  could  not  produce  a  neutral 
salt.  A  part  of  one  or  other  of  the  ingredients  must  remain  uncombined,  or 
else  a  new  kind  of  salt  must  be  formed.  When  oxygen  and  hydrogen  gases 
were  made  to  combine  and  form  water,  you  took  two  volumes  of  hydrogen 
to  one  of  oxygen,  both  of  which  disappeared  entirely;  but  had  you  em- 
ployed a  larger  proportionate  quantity  of  either,  this  excess  would  have 
remained  in  the  gaseous  state  after  the  explosion.  You  told  us  that  such 
would  have  been  the  fact,  and  it  appeared  perfectly  natural(29). 

•Mrs  B.  I  was  fully  aware  that  this  law  would  present  no  difficulty  to  you. 
You  have  mentioned  the  union  of  oxygen  and  hydrogen  forming  water:  do 
you  recollect  that  there  is  another  combination  of  these  principles? 

Caroline.  Perfectly  well.  It  is  called  the  deutoxide,  or  peroxide  of 
hydrogen.  I  remember,  also,  that  when  compared  with  water  it  contains 
just  twice  as  much  oxygen  in  proportion  to  the  hydrogen.  In  decomposing 
this  peroxide,  therefore,  we  should  obtain  equal  volumes  of  oxygen  and 
hydrogen.  There  is  certainly  something  remarkable  in  this,  if  it  be  not 
purely  accidental  (30). 

Mrs  B.  So  far  from  being  accidental,  it  is  believed  to  be  an  individual 
example  of  a  law  which  is  universal ;  namely,  that  -when  gaseous  substances 
unite  together ,  the  volumes  of  the  combining  gases  always  bear  a  simple  ratio  to 
each  other(3l}.  Thus,  to  form  water,  one  volume  of  oxygen  unites  to  two 
of  hydrogen.  To  form  the  deutoxide  of  hydrogen  requires  equal  volumes 
of  the  gases.  When  nitrogen  combines  with  hydrogen,  and  produces  am- 
monia, the  combination  is  in  the  proportion  of  one  volume  of  the  former 
gas  to  three  oHhe  latter.  And  when  sulphurous  acid  is  converted  into  sul- 
phuric acid,  it  is  by  the  condensation  of  two  measures  of  the  acid  gas  and 
one  of  oxygen(32). 

I  might  in  this  way  go  through  the  whole  catalogue  of  those  gases  which 
combine  chemically  with  each  other,  and  show  you  that  their  union  always 
takes  place  in  definite  proportions,  and  in  volumes  which  may  be  measured 
by  the  same  standard. 

Emily.  I  think  I  now  understand  this  law  of  definite  proportions  very  well, 
so  far  as  it  regards  the  union  of  the  gases,  as  of  oxygen  with  hydrogen,  and 
of  hydrogen  with  nitrogen,  in  the  instances  you  have  just  mentioned;  but  in 
the  case  of  acids  and  alkalies,  when  the  bodies  are  either  liquid  or  solid, 
I  do  not  perceive  how  their  bulks  or  volumes  can  be  measured  in  order  to 
ascertain  the  proportion  in  which  they  combine. 

Mrs  B.  Your  observation  is  quite  in  point:  the  fact  is,  that  the  law  of 
combination  by  volume,  does  not  prevail  in  regard  to  liquids  and  solids.  In 
these  we  must  leave  the  circumstance  of  bulk  entirely  out  of  consideration. 
It  is  to  their  -weight  that  we  must  attend,  in  determining  the  proportions  in 
which  they  combine;  and,  accordingly,  if  we  take  the  combining  substances 
in  a  state  of  perfect  purity,  and  ascertain  with  great  accuracy,  once  for  all, 
the  proportions  by  -weight  in  which  they  unite,  we  shall  find  that  in  every 
other  instance  where  these  substances  have  an  opportunity  of  combining,  so 
as  to  produce  the  same  compound,  they  will  unite  in  the  same  proportions 
and  in  no  other.  If  the  same  principles  form  other  compounds,  their  union 
will  be  in  such  proportions  that  one  of  the  bodies  shall  be,  in  weight,  exactly 
double,  triple,  quadruple,  or  in  some  other  exact  multiple  ratio,  to  what  it 
was  in  the  former  combination(33). 


29.  What  considerations  render  the  truth  of  this  law  manifest? 

30.  What  is  noticed  respecting  the  combinations  of  oxygen  and  hydrogen? 

31.  What  is  the  law  relating  to  the  combination  of  gases? 

32.  What  examples  are  given  of  the  truth  of  this  law  ? 

33.  How  does  the  law  of  definite  proportions  apply  to  solids? 


ON  THE  ATOMIC  THEORY.  211 

The  apparent  exceptions  to  this  law  have  been  continually  decreasing  in 
number,  as  more  perfect  methods  of  analyzing  bodies  have  been  discovered, 
and  in  the  minds  of  intelligent  chemists,  not  a  doubt  remains  of  its  univer- 
sality. 

Caroline.  This  law  requires  a  good  deal  of  attention  to  be  well  under- 
stood. The  examples  you  have  given  us  as  regards  the  gases,  appear  suffi- 
cient to  establish  the  fact  of  their  combining  in  measured  volumes;  and  I 
have  no  doubt  you  will  furnish  testimony  equally  satisfactory  respecting 
liquids  and  solids.  I  should  like  to  know,  however,  whether  any  rational 
theory  has  been  devised  to  account  for  these  facts.  Believe  me,  I  have  not 
now  the  temerity  to  inquire  whether  the  cause  is  known. 

Mrs  B.  Your  wish  is  equally  natural  and  proper,  and,  as  far  as  my  ability 
extends,  it  shall  be  gratified.  The  attraction  of  composition,  you  know,  takes 
place  only  between  the  minute  constituent  particles  of  bodies,  that  is,  among 
what  has  been  sometimes  called  their  ultimate  atoms.  Assuming  this  as  a 
fact,  and  admitting  that  all  bodies  consist  of  ultimate  atoms,  which  are  in 
their  natures  indivisible,  Mr  Dalton,  a  very  eminent  English  chemist,  has 
proposed  and  advocated,  with  great  ingenuity,  what  is  called  ,the  ATOMIC 

THEORy(34). 

Emily.  Although  I  am  aware  that  matter  is  divisible  into  particles  incon- 
ceivably minute,  yet  I  cannot  form  any  idea  of  one  of  these  particles  which  is 
not,  in  imagination  at  least,  capable  of  being  divided  into  halves  or  quar- 
ters(35). 

Mrs  B.  It  is  believed  by  many  philosophers,  with  Sir  Isaac  Newton  at 
their  head,  that  matter  is  composed  of  ultimate  particles,  or  atoms,  which 
are  in  their  nature  infinitely  hard,  and  indivisible;  that  by  the  aggregation 
of  such  atoms  similar  in  their  natures,  simple  bodies  are  produced,  and  that 
by  the  combination  of  such  as  are  dissimilar,  compounds  are  formed(36). 
TiJM  a  mass  of  lead  consists  of  innumerable  atoms  of  lead;  and  a  mass  of 
oxide  of  lead  is  formed  of  such  atoms  of  lead,  combined  with  atoms  of  oxygen. 

You  can  very  readily  conceive  that  one  atom  of  lead  may  unite  with  one 
of  oxygen,  and  produce  one  compound  atom,  which  will  of  course  be  an 
oxide  of  lead.  But  as  the  simple  atoms  are  ultimate,  or  indivisible,  the  atom, 
of  lead  cannot  combine  with  one  and  a  fifth  of  oxygen,  although  it  may  unite 
with  two,  three  or  four  atoms(37). 

Caroline.  I  am  delighted  with  the  simplicity  and  the  clearness  of  this 
theory,  and  although  you  may  not  allow  me  to  adopt  it  as  absolutely  true,  I 
cannot  help  believing  in  it  already.  One  atom  of  lead  uniting  with  one  of 
oxygen,  would  of  course  form  a  protoxide;  if  it  combined  with  two  of  oxygen, 
adeutoxide  would  result,  and  if  with  three,  the  combination  would  produce 
a  tritoxide.  Really  I  do  not  see  how  so  perfect  a  theory  can  admit  of  a 
doubt(38). 

Mrs  JB.  It  is  because  it  is  not  susceptible  of  absolute  proof.  We  speak  of 
ultimate  atoms,  and  admit  their  existence  to  be  highly  probable,  but  further 
than  this  we  cannot  go;  we  cannot  examine  these  ultimate  atoms,  milljons 
of  which  may  be  contained  in  the  smallest  visible  particle  of  matter.  Renew- 
ing, therefore,  my  caution  on  the  subject  of  theory,  I  shall  in  future  freely 
use  the  terms  atom  and  atoms,  when  speaking  of  the  proportions  in  which 
bodies  combine,  without  intending  either  to  assert  or  to  deny  the  correct- 
ness of  the  atomic  theory(39). 


#4.  On  what  assumption  is  the  atomic  theory  founded? 

85.  What  remark  is  made  en  the  divisibility  of  particles? 

86.  What  was  the  opinion  of  Newton  respecting  ultimate  particles? 

37.  What  is  said  of  the  combination  of  these  ultimate  particles? 

38.  What  are  the  remarks  of  Caroline  respecting  this  theory? 
69.  Why  may  not  the  truth  of  this  theory  be  fully  admitted? 


212  CONVERSATIONS  ON  CHEMISTRY. 

Emily.  It  seems  to  me  strange  that  the  same  law  should  not  prevail  in 
the  combination  of  bodies,  whether  gaseous  or  solid;  but  that  the  former 
should  combine  in  given  proportions  by  volume,  and  the  latter  in  given  pro- 
portions by  weight. 

Mrs  B.  It  is  certainly  a  very  curious  and  interestirg  fact,  that  the 
combining  volumes  of  the  gases  always  bear  a  simple  ratio  to  each 
other.  But  you  will  readily  perceive  that  these  combinations  are  as  truly 
governed  by  weight  as  are  those  of  solids.  Hydrogen  and  oxygen  unite 
in  given  proportions,  and  form,  water.  When  the  deutoxide  of  hydrogen  is 
to  be  produced,  its  formation  requires  a  double  bulk  or  volume  of  oxygen, 
which  is  evidently  the  same  thing  as  a  double  weight  of  it.  In  treating  of 
the  gases,  therefore,  it  is  as  proper  to  speak  of  their  combination  in  propor- 
tionate weights,  as  it  is  to  represent  them  as  uniting  in  proportionate 
volumes(40).  Water  is  believed  to  consist  of  one  atom  of  hydrogen  united 
to  one  atom  of  oxygen;  and  as  the  fluid  produced  by  their  combination 
weighs  just  nine  times  as  much  as  that  of  the  hydrogen  employed,  it  thence 
follows  that  the  weight  of  one  atom  of  oxygen  must  exceed  that  of  the  atom 
of  hydrogen  eight  fold.  Were  we,  therefore,  to  represent  the  weight  of  an 
atom  of  hydrogen  by  the  number  one,  the  weight  of  an  atom  of  oxygen  would 
be  represented  by  the  number  eight(4l). 

Caroline.  But,  Mrs  B.,  how  can  you  speak  of  weighing  atoms,  after  ad- 
mitting that  they  are  inconceivably  minute.  They  must  be,  practically  at 
least,  as  imponderable  as  light  and  heat  themselves? 

Mrs  B.  I  did  not,  my  dear,  speak  of  "weighing  atoms,  but  of  the  relative 
-weight  of  atoms.  If  I  tell  you  that  water  is  800  times  heavier  than  air, 
I  communicate  a  definite  idea,  although  I  say  nothing  of  the  absolute  weight 
of  either.  If  the  constituents  of  water  unite  atom  to  atom,  each  atom  of 
the  fluid  must  consist  of  one  atom  of  oxygen  and  one  of  hydrogen;  and  these 
compound  atoms,  by  their  accumulation,  produce  sensible  portions  of  w^*r. 
But  the  relative  weights  of  the  oxygen  and  the  hydrogen  must  be  the  same, 
whether  contained  in  a  single  compound  atom,  or  in  the  ocean(42). 

Hydrogen  being  the  lightest  body  known  to  us  in  nature,  its  atom  is  gene- 
rally made  the  standard  with  which  all  other  bodies  are  compared(43).  If 
we  call  the  weight  of  the  atom  of  hydrogen  1,  that  of  oxygen  will  be  8,  that 
of  carbon  6,  of  sulphur  16,  of  potassium  40,  and  of  lead  104(44). 

Emily.  The  mode  of  calculating  the  relative  weights  of  the  atoms  of  oxy- 
gen and  hydrogen  appears  to  me  quite  satisfactory;  but  I  am  entirely  at  a 
loss  to  discover  how  the  relative  weights  of  other  atoms  can  be  deduced 
from  these,  particularly  as  there  are  many  bodies  with  which  hydrogen  does 
not  combine,  as  with  lead  for  example(45). 

Mrs  B.  This  is  a  point  which  I  cannot  fully  explain  without  devoting 
too  large  a  portion  of  time  to  it.  After  supplying  you  with  a  general  idea  of 
the  subject,  I  must  trust  to  your  pursuing  and  applying  it  in  your  future 
studies.  But  to  remove  your  difficulty  respecting  hydrogen  and  lead; 
although  these  do  not  combine,  yet  oxygen  and  lead  combine  in  several  propor- 
tions; and  if  we  can  "discover  how  many  times  the  weight  of  an  atom  of  lead 
exceeds  that  of  an  atom  of  oxygen,  we  can  then  tell  also,  how  much  it  ex.- 


40.  What  is  observed  respecting  the  combination  by  volume  in  gases, 
and  by  weight  in  other  bodies? 

41 .  How  may  the  atomic  weight  of  hydrogen  and  of  oxygen  be  compared  ? 

42.  What  is  observed  respecting  the  weighing  of  atoms? 

43.  Why  has  hydrogen  been  generally  chosen  as  the  standard  of  com- 
parison? 

44.  What  numbers  represent  the  weight  of  certain  atoms? 

45.  What  difficulty  is  stated  respecting  the  estimating  of  these  weights? 


ON  THE  ATOMIC  THEORY.  213 

ceeds  that  of  an  atom  of  hydrogen,  one  of  these  weighing  exactly  eight  times 
as  much  as  the  other. 

Caroline.  I  see  plainly  that  by  knowing  the  ratio  which  exists  between 
Oxygen  and  lead,  and  between  oxygen  and  hydrogen,  that  between  hydrogen 
and  lead  maybe  readily  found. 

Mrs  B.  When  oxygen  and  lead  combine,  and  form  the  protoxide  of 
lead,  which  is  believed  to  consist  of  one  atom  of  each,  every  eight  grains 
of  oxygen  will  produce  one  hundred  and  twelve  grains  of  the  oxide.  Now,  if 
the  weight  of  the  atom  of  oxygen,  which  is  represented  by  the  number  eight, 
be  subtracted  from  that  of  the  atom  of  protoxide  of  lead,  which  is  represented 
by  the  number  one  hundred  and  twelve,  one  hundred  and  four  will  remain 
as  the  weight  of  the  atom  of  lead(46).  In  forming  the  peroxide  of  lead,  one 
hundred  and  four  grains  of  the  metal  combine  with  sixteen  of  oxygen,  and 
the  compound  will  weigh  one  hundred  and  twenty  grains.  In  this,  therefore, 
one  atom  of  lead  has  combined  with  two  atoms  of  oxygen,  and  if  this  per- 
oxide be  heated  to  redness,  it  parts  with  half  its  oxygen,  and  becomes  a  prot- 
oxide(47). 

Emily.  .In  your  illustration  you  speak  of  grains  and  of  atoms,  indifferently, 
as  though  one  would  serve  to  represent  the  other.  I  do  not  clearly  perceive 
how  this  can  be  the  case. 

Mrs  B.  A  little  reflection  will  render  it  perfectly  clear,  and  perhaps 
it  will  be  best  to  recur  to  water  for  the  purpose  of  illustration;  and  you  can 
afterwards  apply  the  same  reasoning  to  oxide  of  lead,  or  to  any  other  com- 
pound. Suppose  you  had  a  sufficient  number  of  atoms  of  hydrogen  to 
weigh  one  grain;  if  you  know  that  an  atom  of  oxygen  weighs  eight  times  as 
much  as  one  of  hydrogen,  you  would  at  once  perceive  that  in  eight  grains  of 
oxygen  there  must  be  precisely  the  same  number  of  atoms  as  in  one  grain  of 
hydrogen.  Suppose  the  number  of  atoms  in  each,  that  is,  in  the  eight  grains 
of  oxygen  and  the  one  grain  of  hydrogen,  to  be  one  million,  then  nine  grains 
of  water  would  contain  two  millions  of  ultimate  atoms,  one  half  of  which  num- 
ber would  be  atoms  of  hydrogen,  which,  at  the  same  time,  would  form  only 
one-ninth  part  of  the  whole  weight.  Whether,  therefore,  we  speak  of  atoms, 
grains,  or  pounds,  the  number  one  would  still  represent  the  weight  of  the 
hydrogen,  and  the  number  eight  that  of  the  oxygen(48). 

In  forming  the  protoxide  of  lead,  consisting  of  one  atom  of  each  of  its  con- 
stituents, the  weight  of  the  lead  is  thirteen  times  as  great  as  that  of  the  oxy- 
gen, and  therefore  one  hundred  and  four  times  as  great  as  that  of  an  atom  of 
hydrogen.  The  numbers  one,  eight,  and  one  hundred  and  four,  will, 
consequently,  represent  their  relative  weights(49). 

Caroline.  I  confess  that  I  do  not  find  this  a  very  easy  part  of  the  sub- 
ject; yet  I  am  fully  impressed  with  its  truth  and  importance,  and  hope  that 
further  inquiry  and  reflection  may  serve  to  remove  the  veil  which  now  par- 
tially obscures  it.  / 

Mrs  B.  I  have  no  fears  upon  this  point;  for  we  shall  have  repeated  oppor- 
tunities of  illustrating  these  atomic  weights,  which  I  shall  be  careful  to  em- 
brace. To  those  I  have  just  given,  I  will  now  add  one^)ther  example  in  the 
two  combinations  of  oxygen  with  carbon,  carbonic  oxide  and  carbonic  acid. 
From  these  you  will  see  why  the  atom  of  carbon  is  represented  by  the  number 
six.  Eight  parts  by  weight  of  oxygen  unite  with  six  of  carbon,  and  produce 
fourteen  of  carbonic  oxide:  this,  in  passing  to  the  state  of  carbonic  acid,  absorbs 


46.  How  is  the  weight  of  an  atom  of  lead  deduced? 

47.  What  is  said  of  the  peroxide  and  protoxide  of  lead? 

48.  How  may  the  absolute  weight  of  a  compound,  and  the  relative  weight 
of  its  atoms  be  computed? 

49.  Why  may  the  numbers  one,  eight,  and  one  hundred  and  four,  repre- 
sent the  relative  weight  of  an  atom  of  hydrogen,  oxygen  and  lead? 


7?  ^ 
214  CONVERSATIONS  ON  CHEMISTRY. 

eight  parts  more  of  oxygen,  producing  twenty-two  of  carbonic  acid.  The  first 
is  formed  by  one  atom  of  oxygen=8,  uniting  to  one  atom  of  earbon=6,  and 
producing  one  atom  of  carbonic  oxide=l4.  Carbonic  acid  consists  of  two 
atoms  of  oxygen  8X2=16,  and  one  atom  of  carbon=6,  making  the  atom  of 
the  acid =22(50). 

Caroline,  But  how  can  you  be  certain  that  the  first  combination  consists 
of  one  atom  of  each;  why  may  there  not  be  two  atoms  of  one,  and  one  of  the 
Other? 

JWrs  B.  It  maybe  shown  upon  mechanical  principles  that  the  most  ener- 
getic attractions  will  be  those  of  particle  to  particle;  and  it  is  therefore  per- 
fectly fair  to  infer,  that  those  chemical  combinations  which  bodies  have  the 
greatest  tendency  to  form,  and  in  which  they  most  resist  decomposition,  are 
of  this  kind,  especially  when  we  find  such  an  inference  borne  out  by  fair 
reasoning,  founded  upon  numerous  experiments(51). 

To  preserve  a  recollection  of  the  examples  which  I  have  given  to  you,  I 
have  set  down  the  substances  and  their"  atomic  weights  in  a  tabular  form, 
which  you  may  examine  at  your  leisure(52). 

Atomic   Weight.       Weight  of  Weight  of  atom 

of  base.  oxygen.        of  compound. 

Water  is  composed  of    Hydrogen       1,          Oxygen    8,  =9 

Deutoxide  of  hydrogen       do  1,  do       16, 2  atoms  =      17 

Protoxide  of  lead  Lead  104,  do         8,  =    112 

Peroxide  of  lead  do  104,  do       16,  2  atoms  =    120 

Carbonic  oxide  Carbon  6,  do         8,  =      14 

Carbonic  acid  do  6,  do       16, 2  atoms  =      22 

For  the  sake  of  simplicity  I  have  confined  each  of  my  examples  to  the 
combination  of  two  simple  bodies  only,  but  the  same  law  prevails  in  the  for- 
mation of  all  compounds,  however  complex  they  may  be. 

Emily.  And  has  the  chemist  been  able  to  derive  any  particular  advantage 
from  the  knowledge  of  the  law  of  definite  proportions? 

Jtfrs  B.  Yes,  and  a  very  considerable  one;  for  it  enables  him  to  form 
tables,  by  which  he  can  see,  at  a  glance,  the  composition  of  all  the  bodies 
which  have  been  accurately  analyzed,  and  ascertain  in  an  instant  what  quan- 
tity of  one  body  will  be  necessary  to  saturate,  or  to  decompose,  a  certain 
quantity  of  another;  and,  in  general,  to  construct  tables  which  serve  to  pre- 
sent, in  one  view,  the  result  of  any  chemical  decomposition,  and  the  quan- 
tities of  the  new  compounds  formed;  by  which  means  a  considerable  saving 
of  labour  is  effected,  whether  in  enabling  us  to  calculate  beforehand  the 
results  of  any  manufacturing  operation,  or  in  estimating  those  obtained  in 
analytical  processes(53).  But  I  perceive  the  subject  is  becoming  rather  too 
intricate  for  us.  We  must  not  run  the  risk  of  entering  into  difficulties 
•which  might  confuse  your  ideas,  instead  of  throwing  additional  light  upon 
this  abstruse  part  of  the  philosophy  of  chemistry. 

. . 

* 

50.  Give  the  example  of  the  combining  proportions  of  oxygen  and  carbon. 

51.  When  do  we  infer  that  a  combination  contains  one  atom  of  each  of  its 
constituents? 

52.  Give  the  atomic  constitution  of  the  compounds  named. 

53.  What  advantage  is  derived  from  the  law  of  definite  proportions? 


ON  THE  CONSTITUTION  OF  THE  ATMOSPHERE.        215 

• 

CONVERSATION  XXI. 

ON  THE  COMBINATIONS  OF  OXYGEN  AND  NITROGEN. 

Five  Combinations  of  Oxygen  and  Nitrogen.  State  of  the  two  Gases  in 
the  Atmosphere.  Oxygen  supplied  by  Gro-wing  Vegetables,  Atomic  Con- 
stitution of  the  Compounds  of  Oxygen  and  Nitrogen.  Nitric  Acid  formed 
by  Nature.  Its  production  by  the  Electric  Spark.  Mode  of  obtaining  it  from 
Nitre.  Charcoal  and  Spirits  of  Turpentine  fired  by  it.  Decomposition  of 
Nitric  Acid  by  Heat  and  Light.  Uses  of  Nitric  Acid. 

Mrs  B.  When  I  inform  you  that  our  attention  to-day  will  be  devoted 
to  the  combinations  of  oxygen  and  nitrogen,  you  will  probably  think  that  we 
are  retrograding  instead  of  advancing  in  our  chemical  inquiries.  You  un- 
doubtedly recollect,  however,  that  in  our  conversation  upon  the  subject  of 
the  atmosphere,  but  little  was  said  respecting  nitrogen  or  its  combinations, 

Caroline.  And  I  must  confess  that  this  same  nitrogen  appeared  to  me 
to  be  so  much  of  a  passive  being,  that  there  was  but  little  to  say  about  it; 
all  the  active  properties  of  the  air  manifestly  depending  upon  its  oxygen. 
We  have  since,  it  is  true,  met  with  nitrogen  in  one  combination  in  which 
it  assumes  no  insignificant  character;  for,  certainly,  as  a  component  part  of 
ammonia,  it  seems  to  be  any  thing  but  inert. 

In  recurring  to  nitrogen,  which  you  have  previously  intimated  enters  into 
other  active  compounds,  and  contributes  its  full  share  to  their  properties,  I 
feel  that,  notwithstanding  the  many  examples  which  we  have  witnessed  of 
the  transforming  power  of  chemical  combination,  I  still  find  it  difficult  fully 
to  realize  its  influence.  I  am,  even  now,  scarcely  prepared  to  anticipate  the 
complete  metamorphosis  which  it  produces  among  our  every  day  acquaint- 
ances, such  as  the  air  we  breathe,  and  the  water  that  we  drink;  although 
these  are  events  with  which  you  have  made  us  in  some  degree  familiar. 

Mrs  B.  The  most  striking  example  of  this  thorough  change  of  proper- 
ties is,  perhaps,  that  upon  the  examination  of  which  we  are  now  entering;  as 
the  component  parts  of  the  atmosphere,  oxygen  and  nitrogen,  unite  together 
in  five  different  proportions,  forming  as  many  well  characterized  compounds, 
three  of  which  are  acids,  and  two  oxides(l). 

Emily.  The  atmosphere,  you  have  told  us,  is  uniform  in  its  composition; 
the  proportionate  quantities  of  oxygen  and  nitrogen  being  the  same  at  all 
times  and  in  all  places.  I  have  often  thought  of  this  fact,  and  have  as  often 
been  at  a  loss  to  account  for  it.  There  are.  so  many  processes  by  which  the 
oxygen  of  the  atmosphere  is  separated  from  it,  and  made  to  combine  with 
other  bodies,  that  a  constant  variation  in  its  amount  might  be  expected. 

Mrs  B.  The  air  of  the  atmosphere  is  not  reckoned  among  the  five  com- 
pounds to  which  I  have  alluded,  as  it  is  generally  believed,  that,  notwith- 
standing the  uniformity  of  its  constitution,  the  gases  of  which  it  consists  are 
in  a  state  of  simple  mixture(2).  The  arguments  in  favour  of  its  being  a 
chemical  combination,  rest  upon  the  fact,  that  the  oxygen  is  to  the  nitrogen 
precisely  in  the  proportion  of  one  to  four,  by  volume,  whilst  their  atoms  are, 
in  number,  as  one  to  two;  agreeing  in  every  respect  with  the  law  of  definite 
proportions(3). 


1.  How  many  chemical  combinations  are  there  of  oxygen  and  nitrogen? 

2.  Is  it  believed  that  they  are  chemically  combined  in  the  atmosphere? 

3.  What  circumstance  favours  the  idea  of  their  chemical  combination? 


216  CONVERSATIONS   ON  CHEMISTRY. 

Caroline.  I  should  think  this  proof  sufficient,  as  these  exact  proportions 
could  not  be  the  result  of  mere  accidental  mixture. 

Mrs  B.  There  was  no  doubt  design  in  thus  constituting  the  atmos- 
phere. But  abler  chemists  than  we  are  have  considered  the  proofs  of  sim- 
ple mixture  to  be  sufficient  to  establish  the  fact.  If  we  take  oxygen  and 
nitrogen,  and  mix  them  in  the  proportions  in  which  they  are  found  in  the 
atmosphere,  the  temperature  will  be  unaffected,  the  specific  gravity,  and 
indeed  all  the  sensible  qualities  of  the  mixture  will  be  precisely  those  of 
common  air.  There  is,  consequently,  not  the  slightest  evidence  that  any 
chemical  action  has  taken  place(4). 

Caroline.  I  find  that  I  ought  to  have  heard  both  sides  of  the  question  before 
giving  my  opinion.  I  should  like,  however,  to  know  how  nature  supplies  the 
oxygen  which  is  lost  in  combustion,  in  respiration,  and  in  other  processes 
•which  decompose  the  atmosphere. 

J\frs  B.  It  is  probable  that  growing  vegetables  are  the  principal,  if  not 
the  only  agents  employed  in  effecting  this  purpose.  During  the  day,  a  healthy 
plant  absorbs  carbonic  acid  from  the  atmosphere,  and  gives  out  oxygen.  la 
the  night,  it  is  true,  the  reverse  operation  takes  place,  oxygen  being  absorbed 
and  carbonic  acid  evolved,  but  still  not  in  quantities  sufficient  to  counteract 
the  first  effect(5). 

As  regards  the  other  compounds  of  oxygen  and  nitrogen,  you  will  find 
evidence  enough  of  their  chemical  union.  The  gases  of  which  they  consist 
may  be  mixed  together  in  the  five  proportions  in  which  they  can  be  made  to 
combine,  but  will  not  in  this  state  acquire  any  of  those  properties  which 
so  strongly  characterize  them  when  their  atoms  have  united  by  chemical 
attraction(6). 

Emily.  I  am  glad  that  we  have  acquired  some  knowledge  of  the  atomic 
theory,  as  it  will  undoubtedly  enable  us  to  trace  these  various  combinations 
more  perfectly  than  we  could  have  done  without  such  information. 

J\frs  J3.  That  was  my  principal  motive  for  deferring  the  consideration  of 
these  compounds  until  the  present  period,  as  they  will  serve  to  exemplify 
the  use  of  this  theory  in  a  very  satisfactory  manner.  The  weight  of  an 
atom  of  nitrogen  has  been  found  to  be  fourteen;  that  of  oxygen,  you  will 
recollect,  is  eight,  hydrogen  being  one;  or  in  other  words,  an  atom  of  oxygen 
is  eight  times,  and  an  atom  of  nitrogen  fourteen  times,  as  heavy  as  an  atom  of 
hydrogen(7).  The  compounds  of  nitrogen  and  oxygen  increase  regularly  from, 
one  atom  of  nitrogen  with  one  of  oxygen,  up  to  one  of  nitrogen  with  five  of 
oxygen.  They  are  exhibited  in  this  table,  which  you  should  copy  and  preserve, 
until  you  recollect  the  numbers. 

Composed  of 
Nitrogen.      Oxygen. 

1.  Protoxide  of  nitrogen,  or  nitrous  oxide,     1  atom  -{-  1  atom. 

2.  Deutoxide  of  nitrogen,  or  nitric  oxide,  i  atom  -f-  2  atoms. 

3.  Hyponitrous  acid,  -         -         -  1  atom  -f  3  atoms. 

4.  Nitrous  acid,  ...         -          1  atom  -j-  4  atoms. 

5.  Nitric  acid, 1  atom  +  5  atoms(8). 

Caroline.    And  we,  it  seems,  are  inhaling,  at  every  breath,  the  elements 

of  all  these  different  compounds.  It  appears  a  little  surprising  that  two 
substances  which  are  capable  of  uniting  in  so  many  different  proportions, 
should  still  remain  merely  mixed  together,  as  they  do  in  the  atmosphere. 


4.  What  are  the  facts  which  militate  against  this  opinion? 

5.  From  what  source  is  the  waste  of  oxygen  probably  supplied? 

6.  What  is  remarked  respecting  the  five  known  combinations? 

7.  What  is  the  atomic  weight  of  nitrogen,  hydrogen  being  one? 

8.  How  are  the  compounds  of  oxygen  and  nitrogen  constituted? 


ON  THE  COMPOUNDS  OF  OXYGEN  AND  NITROGEN.    217 

JWrs  B.  The  repulsive  agency  of  the  caloric,  which  is  combined  with 
them  in  the  gaseous  state,  completely  counteracts  their  chemical  attraction 
for  each  other.  But  when  one  or  both  of  them  are  in  the  nascent  state,  they 
readily  unite(9).  Although  oxygen  and  nitrogen  are  capable  of  forming  these 
five  several  compounds,  only  one  of  them  is  known  as  a  natural  product,  and 
that  is  the  nitric  acid.  All  the  others  are  artificially  obtained  by  the  chemist 
in  his  laboratory;  and,  in  most  instances,  by  the  direct  decomposition  of  this 
acid(10). 

Emily.  All  that  is  necessary  to  convert  nitric  into  nitrous  acid,  must  be 
to  deprive  the  former  of  one-fifth  of  its  oxygen;  and  it  is  plain  that  upon 
the  same  principle,  all  the  other  compounds  may  be  obtained.  This  indeed 
is  a  most  satisfactory  illustration  of  the  atomic  theory(ll). 

Caroline.  Nitrogen,  from  its  combination  with  oxygen,  would  seem  to 
claim  a  place  among  the  combustibles,  yet  I  have  no  recollection  of  any  fact 
which  shows  that  it  is  capable  of  being  burnt,  although  it  can  be  oxygenated 
in  so  many  different  proportions. 

Mrs  B.  Nitrogen  is  a  body  which  seems  to  stand  alone  in  its  relation- 
ship, both  to  combustibles  and  to  supporters  of  combustion,  as  it  cannot  be 
classed  with  either.  It  does  not  support  combustion;  and  whilst  it  unites 
with  oxygen  and  with  the  other  bodies  which  do  support  it,  it  does  this 
without  the  disengagement  of  light  and  heat,  which  you  know  are  the  essen- 
tial characteristics  of  combustion(12). 

In  examining  the  compounds  of  oxygen  and  nitrogen,  we  shall  commence 
with  the  last  upon  the  list,  that  is,  NITRIC  ACID.  This  acid,  I  have  in- 
formed you,  is  presented  to  us  ready  formed  by  nature,  and  all  the  other 
compounds  may  be  obtained  by  its  decomposition,  simply,  as  Emily  observes, 
by  depriving  it  of  different  portions  of  its  oxygen.  You  ought  to  know, 
however,  that  the  chemist  can  produce  nitric  acid  by  effecting  the  direct  com- 
bination of  its  elements,  as  they  exist  in  the  atmosphere.  If  a  mixture 
of  oxygen  and  nitrogen  be  confined  in  a  glass  tube,  and  a  succession  of 
electric  sparks  be  made  to  pass  through  the  tube,  the  bulk  of  the  gases 
will  be  found  gradually  to  diminish,  and  after  several  thousand  electrical 
discharges,  a  minute  quantity  of  nitric  acid  will  be  obtained(lS).  This 
experiment  was  first  performed  by  Dr  Priestley,  but  we  are  indebted  to  the 
repetition  of  it  by  the  eminent  chemist  Mr  Cavendish,  for  the  correct 
deduction  that  nitric  acid  is  composed  of  the  bases  of  oxygen  and  nitrogen 
gases(l4). 

Caroline.  If  the  electric  fluid  causes  the  gases  to  unite,  why  is  there  not 
a  portion  of  nitric  acid  formed  in  the  atmosphere  in  a  thunder  storm,  when 
the  lightning  repeatedly  passes  through  it?  We  should  be  in  a  sorry  con- 
dition if  such  a  storm  should  at  once  convert  the  air  into  nitric  acid. 

•Mrs  B.  There  i  s  no  danger  of  this,  my  dear.  The  lightning  can  affect  but 
a  very  small  portion  of  the  atmosphere;  and  it  appears  that  many  thousand 
discharges  through  the  same  portion  are  necessary  to  the  production  of  the 
acid.  The  quantity  of  oxygen  in  the  atmosphere,  also,  is  too  small  to  favour 
its  formation,  and  if  there  were  any  produced  in  this  way,  it  must  be  much 
too  small  a 'quantity  to  be  perceptible(lS). 

You  have  formerly  told  us  that  what  is  called  aquafortis   is 


9.  Why  do  they  not  combine  in  their  state  of  mixture  ? 

10.  Which  of  these  combinations  is  found  ready  formed  in  nature? 

11.  What  observations  are  made  on  the  production  of  nitrous  acid? 

12.  What  is  remarked  respecting  the  classing  of  nitrogen? 

13.  In  what  way  may  nitric  acid  be  directly  formed? 

14.  To  whom  are  we  indebted  for  this  discovery? 

15.  Why  is  not  nitric  acid  produced  by  lightning? 

T 


218 


CONVERSATIONS  ON  CHEMISTRY. 


nitric  acid.  As  this  is  extensively  used  in  the  arts,  there  must  be  some  very 
ready  means  of  obtaining  it  from  its  natural  combinations,  whatever  they 
may  be. 

J\frs  JS.  The  salt  which  is  known  to  you  under  the  name  of  nitre  or  salt- 
petre, is,  in  chemical  language,  the  nitrate  of  potassa,  and  consists  of  nitric 
acid  united  to  potassa.  It  is  from  this  salt  that  the  acid  is  obtained.  Sul- 
phuritf  acid  has  so  strong  an  affinity  to  potassa,  that  it  will  readily  combine 
with  it,  and  exclude  the  nitric  acid.  I  will  now  exhibit  the  process  by 
•which  nitric  acid  is  procured;  as  several  of  the  acids  and  some  other  com- 
pounds are  obtained  iu  a  similar  way(16). 

You  see  that  I  use  a  retort  and  receiver,  resembling  those  formerly  shown 
to  you.  Into  the  retort  I  put  a  few  ounces  of  nitre,  and  pour  upon  it  about 
an  equal  weight  of  sulphuric  acid;  when  I  adapt  a  receiver  to  the  retort,  and 
apply  heat  to  the  materials  contained  in  it.  As  the  nitric  is  disengaged  by  the 
sulphuric  acid,  the  heat  will  convert  it  into  vapour,  which  will  distil  over; 
and  as  the  receiver  is  kept  cold,  it  will  then  be  condensed  into  the  liquid 
form(17). 

Preparation  of  Nitric  Acid. 


A  B 

[A,  lamp  placed  under  the  retort,  which  contains  nitrate  of  potassa  (nitre) 
and  sulphuric  acid.  B,  stand  supporting  the  receiver,  in  which  the  nitric 
acid  is  to  be  collected.] 

I  place  the  apparatus  under  the  chimney,  because  a  considerable  portion 
of  corrosive,  uncondensable  vapour  will  be  disengaged  in  the  process. 

Caroline.     Are  we  to  consider  aquafortis  and  nitric  acid  as  identical, 
or  is  there  any  difference  between  them? 

•Mrs.  J$.  Aquafortis  is  a  weak,  and,  generally,  an  impure  nitric  acid;  its 
strength  being  only  one-fourth  as  great  as1  that  of  the  perfect  acid.  It  re- 
ceived from  the  alchemists  the  name  of  aquafortis  (strong  water),  in  conse- 
quence of  its  effectually  dissolving  the  greater  number  of  the  metals,  as  well 
as  various  other  substances.  Aquafortis  is  better  adapted  to  many  pur- 
poses in  the  arts  than  the  pure  acid,  and  it  forms,  therefore,  a  special  article 
of  manufacture(l  8). 

Emily.  You  have  already  taught  us  something  of  the  solvent  power  of 
nitric  acid,  and  I  believe  you  informed  us  that  it  is  principally  indebte4 
for  this  power  to  the  facility  with  which  it  parts  with  its  oxygen. 


16.  From  what  substance,  and  by  what  means  is  nitric  acid  obtained? 

17.  Describe  the  apparatus  and  the  process  employed. 

18.  What  is  said  respecting  nitric  acid  and  aquafortis? 


ON  NITRIC  ACID.  219 

Mrs  B.  I  did.  This  acid  contains  a  larger  quantity  of  oxygen  than  any 
other,  and  retains  it  by  an  attraction  so  feeble  that  it  is  decomposed  by 
almost  every  substance  having  an  affinity  for  it(19).  Some  which  attract  it 
strongly,  will  combine  with  the  whole  contained  in  the  acid,  and  liberate  its 
nitrogen  in  the  gaseous  form.  Others,  which  act  with  less  energy,  take  away 
a  portion  only  of  the  oxygen,  leaving  the  remaindeu  in  combination  with  the 
nitrogen,  and  thus  producing  one  of  the  less  oxygenated  compounds(20). 

Caroline.  If  nitric  acid  parts  so  readily  with  its  oxygen,  may  it  not  ac- 
tually produce  combustion  in  those  substances  which  are  the  most  inflamma- 
ble? 

Mrs  B.  In  most  cases  the  decomposition  is  not  sufficiently  rapid  to  pro- 
duce actual  inflammation,  although  it  does  so  in  a  few  instances.  If  we  take 
some  perfectly  dry  fresh  burnt  charcoal,  pulverize  it,  put  it  into  a  glass,  and 
then  pour  upon  it  some  of  the  strongest  nitric  acjd,  a  vivid  inflammation  will 
ensue,  and  a  suffocating  vapour  will  escape,  consisting  of  carbonic  acid  and 
the  decomposed  nitric  acid(21).  All  the  essential  oils  likewise  maybe  in- 
flamed by  it.  This  effect  I  will  exhibit  to  you,  using  the  oil  of  turpentine.  For 
this  purpose  I  put  some  of  it  into  a  warm  saucer;  and,  from  a  glass  at  the  end 
of  a  long  rod,  pour  on  it  strong  nitric  acid,  the  oxygen  of  ^vhich  will  unite  to 
the  oil  with  such  rapidity  as  to  inflame  it.  It  is  necessary  to  stand  at  a 
distance  to  avoid  danger  from  the  flame.  The  essential  oils  consist  princi- 
pally of  hydrogen  and  carbon,  and  the  oxygen  of  the  acid  unites  with  each 
of  them  in  this  combustion(22). 

Spirits  of  Turpentine  inflamed  by  Nitric  Acid. 


Emily.  Have  we  any  means  of  decomposing  the  nitric  acid  so  as  to  con- 
vert it  entirely  into  nitrogen  and  oxygen  gases? 

Mrs  B.  The  very  same  means  by  which  most  combustibles  are  made  to 
unite  with  oxygen  and  are  converted  into  acids,  will  serve  completely  to  de- 
compose the  nitric  acid:  I  allude  to  a  great  elevation  of  temperature.  If  a 
portion  of  its  vapour  be  passed  through  a  red-hot  tube  of  earthenware,  it 
will  be  entirely  converted  into  oxygen  and  nitrogen  gases,  which  will  be  found 
mixed  in  the  proportions  before  mentioned(23).  Such  is  the  quantity  of  oxy- 
gen thus  produced,  that  a  taper  which  has  been  just  blown  out,  will  be 
relighted  if  plunged  into  the  mixed  gases. 

Even  the  light  of  the  sun  alone  will  produce  a  partial  decomposition  of 
nitric  acid.  That  which  I  have  in  this  bottle  was  as  limpid  and  colourless  as 


19.  Upon  what  does  the  solvent  power  of  nitric  acid  appear  to  depend.' 

£0.  How  do  different  substances  operate  upon  this  acid? 

21.  What  effect  will  nitric  acid  produce  upon  fresh  burnt  charcoal? 

22.  How  may  spirits  of  turpentine  be  inflamed  by  it? 

23.  In  what  way  may  nitric  acid  be  completely  decomposed? 


220  CONVERSATIONS  ON  CHEMISTRY. 

water,"  when  I  first  brought  it  from  a  dark  closet  into  this  room.  It  has 
already,  you  perceive,  assumed  a  pale  straw  colour,  and  by  continued  ex- 
posure to  light  it  will  acquire  a  still  darker  hue(24). 

Emily.  But  it  has  been  kept  closely  stopped,  so  that  nothing  could 
escape  from  it  into  the  air,  nor  could  the  air  have  access  to  it;  and  under 
these  circumstances,  it.  is  difficult  to  see  how  a  decomposition  could  be 
effected. 

Mrs  S.  Had  the  glass  been  hermetically  sealed,  the  same  effect  would 
have  ensued.  And  it  is  evident  that  it  is  produced  by  light  itlone,  as  it  does 
not  take  place  in  the  dark,  whatever  change  of  temperature  may  occur.  This 
fact  seems  to  prove  that  light  as  well  as  heat  is  a  constituent  of  oxygen  gas, 
the  gas  being  disengaged  from  the  acid,  and  found  occupying  the  upper  part 
of  the  bottle(25). 

If  colourless  nitric  acid  be  put  into  a  retort,  the  beak  of  which  is  placed 
under  a  receiver  in  the  pneumatic  cistern,  the  action  of  light  will  cause 
bubbles  of  oxygen  gradually  to  escape,  and  to  pass  into  the  receiver,  whilst 
the  acid  will  become  coloured.  The  source  of  this  colour  will  be  hereafter 
explained  to  you(26). 

Caroline.  As  nitric  acid,  under  the  name  of  aquafortis,  is  so  extensively 
used  in  the  arts,  it  would  be  interesting  to  learn  the  purposes  to  which  it  is 
principally  applied. 

J\frs  B.  Its  uses  are  numerous,  but  I  can  only  give  you  a  general  idea 
of  them.  It  is  largely  employed  in  refining,  and  many  other  operations  on 
the  metals.  Most  of  the  beautiful  landscapes  and  other  subjects  printed 
from  copper  plates,  are  etched  upon  the  copper  by  its  means.  In  the 
hands  of  the  dyer,  it  serves  to  fix  and  to  heighten  a  variety  of  colours.  In 
chemical  processes,  its  uses  are  very  numerous?  and  to  the  physician  it  is  a 
valuable  auxiliary  in  the  cure  of  many  diseases(27).  We  must  now  dismiss 
this  part  of  our  subject,  and  proceed  to  some  of  the  substances  produced  by 
the  decomposition  of  nitric  acid.  But  as  I  have  more  to  say  respecting  them 
than  can  well  be  included  in  one  conversation,  we  will  adjourn  until  to- 
morrow. 


24.  What  effect  is  produced  upon  this  acid  by  light? 

25.  What  proves  that  this  change  is  produced  by  light  alone? 

26.  How  may  the  oxygen  which  light  disengages  be  collected? 

27.  What  are  the  principal  uses  to  which  nitric  acid  is  applied? 


NITRIC  OXIDE.  221 


CONVERSATION  XXII. 

ON  THE  COMBINATIONS   OF  OXYGEN  AND  NITROGEN  (CON- 
TINUED,) AND  ON  NITRATES. 

Synthetical  and  Analytical  Examination  of  ^Bodies.  Nitrate  of  Copper. 
Nitric  Oxide,  Deutoxide  of  Nitrogen,  or  Nitrous  Jlir.  Nitrous  Acid. 
Eudiometrical  Property  of  Nitrous  Jlir.  Combustion  in  it.  Absorbed  by 
Nitric  Acid.  Aquafortis.  Hyponitrous  Acid.  Nitrous  Oxide.  Forma' 
tion  and  decomposition  of  Nitrate  of  Ammonia.  Combustion  in  Nitrous 
Oxide.  Its  effects  -when  inhaled.  Table  of  the  Compounds  of  Oxygen  and 
Nitrogen.  Nitrate  of  Potassa,  Nitre,  or  Saltpetre.  Nitrate  of  Lime. 
Nitre  Caves.  Incombustibility  of  Nitre.  Oxygen  Gas  obtained  from  if. 
Deflagration.  Gunpotvder.  Detonation.  Fulminating  Powder.  Uses  of 
Nitre.  Properties  of  the  Nitrates.  Combustion  of  Tin  Foil  by  Nitrate 
of  Copper. 

Emily.  As  there  are  five  different  combinations  of  oxygen  and  nitrogen, 
and  you  have  commenced  with  the  most  powerful  of  the  series,  Nitric  acid, 
I  suppose  that,  proceeding  by  a  descending  scale,  we  are  next  to  learn  how- 
to  deprive  this  compound  of  one  proportional  of  its  oxygen,  and  thus  to 
reduce  it  to  the  state  of  nitrous  acid. 

JUrs  H.  There  are  two  modes  of  examining  chemical  substances;  the 
synthetical  and  the  analytical.  When  we  proceed  by  the  former  method, 
we  take  the  simples  of  which  a  body,  under  consideration,  consists;  com- 
bine these  simples  together,  and  obtain  their  product.  By  the  analytical 
mode,  we  take  a  compound  as  it  is  presented  to  us;  inquire  into  its  proper- 
ties, and  then  proceed  to  analyze  it,  that  we  may  learn  what  are  its  con- 
stituents^). We  have  hitherto  pursued  the  former  course,  but  in  the  pre- 
sent instance  we  shall  adopt  the  latter.  Proceeding  regularly,  the  proper- 
ties of  nitrous  acid  would  come  next  in  order  for  our  examination,  but  it 
will  accord  best  with  the  course  of  our  experiments  to  pas?  this  by,  until  we 
have  attended  to  the  gas  called  NITRIC  OXIDE,  which  we  can  readily  obtain 
by  depriving  the  acid  of  three  proportionals  of  its  oxygen. 

Emily.  We  shall  be  perfectly  satisfied  to  follow,  in  whatever  course  you 
may  choose  to  lead  us,  as  we  are  sure  that  it  will  be  that  which  is  best  fitted 
for  our  instruction. 

JUrs  S.     In  our   first  conversation,  Procuring  Nitric  Oxide. 

I  exhibited  to  you  the  experiment  of 
dissolving  copper  in  sulphuric  acid,  to 
which  a  little  nitric  acid  had  been  added. 
By  this  means  we  produced  a  sulphate  of 
copper  (blue  vitriol,)  (page  19.)  The  use 
of  the  nitric  acid  in  this  case  was  to  afford 
oxygen  to  the  copper,  which,  when  con- 
verted into  an  oxide,  was  dissolved  by 
the  sulphuric  acid(2).  I  am  now  about 
to  dissolve  some  copper  in  nitric  acid 
alone;  we  shall  by  this  means  obtain  ni- 
trate of  copper.  This  glass  flask,  or  gas 


1.  What  are  the  two  modes  of  examining  chemical  substances? 

2.  What  is  said  respecting  the  production  of  sulphate  of  copper? 

T  2 


222  CONVERSATIONS  ON  CHEMISTRY. 

bottle,  as  it  is  called,  I  use  instead  of  a  retort.  I  have  put  into  it  some  shreds  of 
copper,  and  upon  these  I  pour  nitric  acid  a  little  diluted  with  water.  This  will 
immediately  begin  to  act  upon  the  copper  with  greatpower,  and  a  quantity 
of  gas  will  escape,  which  we  will  collect  in  a  receiver  in  the  usual  way.  A 
solution  of  nitrate  of  copper  will  remain  in  the  bottle(3). 

Caroline.  This  is  the  same  mixture  you  made  in  our  first  conversation 
on  the  metals,  (p.  185,)  and  I  recollect  that  a  very  deep  orange-coloured 
vapour  escaped  from  it;  but,  in  the  present  instance,  the  gas  collected  in  the 
receiver  is  perfectly  colourless(4). 

Mrs  B.  You  will  soon  learn  the  cause  of  this  difference  in  colour.  The 
gas  which  we  have  now  collected  is  the  deutoxide  of  nitrogen,  or  nitric 
oxide.  Dr  Priestley,  its  discoverer,  called  it  nitrous  air,  a  name  still  fami- 
liarly used(5).  Water  absorbs  nitric  oxide  so  sparingly,  that  it  may  be 
kept  in  contact  with  that  fluid  for  any  length  of  time.  By  recurring  to  your 
table,  you  will  find  that  it  contains  two  atoms  of  oxygen  to  one  of  nitrogen, 
and  indeed  its  appellation  of  deutoxide  indicates  this  fact(6).  It  has  so 
strong  an  attraction  for  oxygen  as  to  combine  with  it  by  mere  mixture.  If, 
therefore,  we  suffer  it  to  come  in  contact  with  the  atmosphere,  it  immedi- 
ately loses  its  character  as  an  oxide;  for  it  instantaneously  deprives  the  air  of 
so  much  oxygen  as  to  double  its  own  portion,  and  thus  assumes  the  form  of 
NITHOITS  ACID.  This  acid,  in  its  pure  state,  is  also  a  gas,  but  one  which 
is  readily  absorbed  by  water(7). 

Caroline.  Then  I  suppose  that  the  orange  red  fumes  which  escaped  in 
the  former  experiment  were  those  of  nitrous  acid,  and  that  the  colour  was 
produced  by  the  union  of  the  oxygen  of  the  atmosphere  with  the  deutoxide 
of  nitrogen. 

Mrs  B.  Your  conjecture  is  perfectly  correct.  I  will  now  incline  the 
receiver  on  one  side  sufficiently  to  allow  a  bubble  of  the  gas  to  escape  into 
the  atmosphere,  and  you  will  see  that  it  instantaneously  assumes  a  deep 
orange  colour(8). 

Emily.  How  curious!  and  yet  the  gas  within  the  glass  is  perfectly  in- 
visible. This,  however,  would  become  coloured  were  you  to  admit  a  few 
bubbles  of  oxygen  or  atmospheric  air,  would  it  not? 

Mrs  B.  Certainly;  and  to  exhibit  this  effect,  I  will  now  mix  with  it 
a  small  portion  of  oxygen. 

Emily.  The  whole  volume  of  the  gas  has  become  coloured,  and  the 
water  is  rising  rapidly  in  the  receiver.  This  must  be  owing  to  the  forma- 
tion of  nitrous  acid,  and  its  absorption  by  the  water(9). 

Caroline.  Could  you  not  add  to  this  nitric  oxide  such  a  portion  of  oxy- 
gen as  should  convert  the  whole  of  it  into  nitrous  acid?  In  this  case  I 
should  expect  to  see  the  absorption  complete,  and  the  glass  filled  with 
water. 

Mrs  B.  Were  the  two  gases  perfectly  pure,  and  mixed  in  the  exact 
proportions  which  form  nitrous  acid,  the  result  would  be  such  as  you  have 
supposed. 

This  effect  is  a  very  curious  one;  for,  suppose  the  receiver  to  contain 
two  pints  of  nitric  oxide  gas;  if  to  this  be  added  one  pint  of  oxygen 


3.  Describe  the  mode  of  forming  a  solution  of  the  nitrate  of  copper. 

4.  What  remark  is  made  respecting  this  and  a  former  experiment? 

5.  What  gas  is  collected,  and  who  was  the  discoverer  of  it? 

6.  Is  nitric  oxide  absorbed  by  water,  and  what  is  its  composition? 

7.  Describe  the  mode  of  converting  it  into  nitrous  acid. 

8.  What  particular  appearance  accompanies  the  formation  of  this  acid? 

9.  What  effects  are  produced  when  oxygen  is  admitted  into  a  receiver 
filled  with  this  gas? 


ON  THE  DEUTOXIDE  OF  NITROGEN.  223 

gas,  instead  of  the  quantity  of  air  being  increased  by  this  addition,  both  the 
gases  will  disappear  entirely(lO). 

Nitric  oxide  has  been  used  in  eudiometry,  in  consequence  of  its  property 
of  combining  with  oxygen;  but  the  eudiometrical  processes,  which  I  for- 
merly described  to  you,  (p.  149,)  have  been  found  to  be  more  accurate  and 
convenient.  The  mode  of  employing  the  nitrous  air  will  be  suggested  to 
you  by  the  last  experiment(ll). 

Caroline.  From  the  quantity  of  oxygen  contained  in  the  deutoxide  of 
nitrogen,  I  should  apprehend  that  it  would  support  combustion  much  bet- 
ter than  atmospheric  air. 

•Mrs  It.  Recollect  that  the  oxygen  is  not  free,  but  combined  with  nitro- 
gen; and  that  nitrous  air,  instead  of  having  a  disposition  to  part  with  it3 
oxygen,  has  a  tendency  to  acquire  more.  Gases  do  not  support  combustion 
merely  because  they  contain  oxygen, but  because  they  are  ready  to  part  with 
it.  A  burning  candle,  and  indeed  most  other  burning  bodies  are  extinguished 
when  imnversed  in  the  deutoxide.  Some,  however,  which  have  a  very  strong 
attraction  for  oxygen,  will  decompose  it.  Phosphorus,  for  example,  will 
burn  in  it  very  brilliantly,  the  products  of  the  combustion  being  phosphoric 
acid  and  nitrogen(12). 

The  deutoxide  of  nitrogen  is  said  to  be  irrespirable,  and  there  is  but  little 
doubt  of  the  fact;  but  this  we  have  no  means  of  ascertaining,  as  by  mixing 
with  the  air  contained  in  the  mouth  and  lungs  it  becomes  nitrous  acid,  which 
is  extremely  corrosive,  and  must  quickly  produce  death  from  this  cause, 
even  if  it  did  not  from  suffocation(lS). 

Emily.  When  nitric  acid  was  decomposed  by  the  action  of  light,  the 
colour  produced  in  it  must  have  arisen  from  the  formation  of  some  nitrous 
acid  by  the  abstraction  of  oxygen  from  the  nitric  acid. 

Mrs  B.  Your  conclusion  is  a  very  natural  one,  but  not  perfectly  cor- 
rect. When  nitric  acid  is  partially  decomposed,  it  usually  yields  up  so 
much  of  its  oxygen  as  to  pass  into  the  state  of  nitric  oxide,  and  this  appears 
to  be  the  case  when  light  is  the  decomposing  agent.  The  colour  in  the 
acid  results,  therefore,  from  the  admixture  of  nitric  oxide(l4). 

Caroline.  But  certainly  there  must  be  some  nitrous  acid  formed,  as  is 
plainly  indicated  by  the  colour;  nitrous  air,  being  itself  without  colour, 
could  not  change  that  of  the  nitric  acid. 

Emily.  Perhaps  that  is  asserting  a  little  too  much,  as  we  have  seen 
colour  produced  by  the  mixture  of  two  colourless  articles,  and  may  not  that 
be  the  case  in  the  present  instance(15)? 

J\frs  B.  It  evidently  is  the  case;  for  nitric  acid  will  absorb  a  large 
quantity  of  nitrous  air,  and  it  changes  its  colour  progressively  as  the  absorp» 
tion  goes  on.  When  the  quantity  of  the  gas  is  small,  its  hue  is  that  of  a 
pale  yellow,  and  as  the  quantity  increases  it  will  become  of  a  bright  yellow, 
then  a  deep  orange,  and  at  last  will  appear  green.  Heat  will  expel  the  gas 
unchanged;  and  merely  diluting  the  acid  with  water  will  produce  the  same 
effect(16). 

What  is  found  in  commerce  under  the  name  of  aquafortis,  or  nitrous 
acid,  is  usually  coloured,  and  consists  of  nitric  acid  holding  variable  quan- 
tities of  nitrous  air  in  solution(l7). 


10.  How,  and  why,  may  both  these  gases  be  made  to  disappear? 

11.  For  what  purpose  has  nitrous  air  been  sometimes  employed? 

12.  How  does  this  gas  operate  in  supporting  combustion? 

13.  What  is  said  respecting  its  respirability  ? 

14.  How  does  light  affect  colourless  nitric  acid? 

15.  What  is  remarked  respecting  this  production  of  colour? 

16.  How  may  it  be  proved  that  nitrous  air  produces  the  colour? 

17.  Jlquafortis  is  generally  coloured,  from  what  does  this  proceed? 


224  CONVERSATIONS  ON  CHEMISTRY. 

Caroline.  How  necessary  it  is  to  learn  facts  before  we  form  opinions. 
But,  Mrs  B.,  according  to  our  table,  there  is  an  acid  intermediate  between 
nitrous  acid  and  nitric  oxide,  about  which  we  have  not  yet  learnt  any 
thing. 

Mrs  B.  Nor  is  there  much  for  you  to  learn,  as  but  little  is  known  re- 
specting the  HTPOKITROUS,  or  SUBTSUTBOUS,  ACID,  as  it  is  sometimes  called. 
The  existence  of  such  a  compound  has  been  sufficiently  proved,  but  it  has 
not  been  obtained  in  an  uncombined  state,  nor  are  there  any  facts  respect- 
ing it  which  I  think  it  necessary  to  detail(18). 

Emily.  Then  the  PROTOXIDE  op  NITROGEN,  or  STITROTTS  OXIDE,  will,  I 
believe,  complete  our  catalogue  of  these  compounds.  The  nitrous  oxide 
is  the  same  with  the  exhilarating  gas,  which,  when  inhaled,  produces  such 
extraordinary  effects,  is  it  not? 

Mrs  JR.  It  is.  This  gas  was  discovered  by  Priestley,  but  we  are  indebted, 
to  Davy  for  a  full  examination  of  its  properties,  and  for  the  process  by 
which  it  is  obtained  in  a  pure  state(19).  It  was  formerly  procured  by  ex- 
posing nitric  oxide  to  the  filings  of  zinc  moistened  with  water;  or  to  some 
other  substance  which  would  deprive  it  of  one-half  of  its  oxygen.  Zinc  or 
iron,  when  dissolved  in  nitric  acid,  seizes  upon  so  large  a  portion  of  its  oxy- 
gen as  to  reduce  it  to  the  state  of  nitrous  oxide.  When  procured,  how- 
ever, by  either  of  these  processes,  it  is  always  mixed  with  a  portion  of  the 
deutoxide,  which  renders  it  irrespirable(20).  But  it  can  be  obtained  pure 
by  decomposing  a  salt  called  the  NITRATE  or  AMMOKIA,  the  name  of  which 
will,  at  once,  suggest  to  you  its  composition,  although  it  has  never  been 
explained  to  you. 

Emily.  How  greatly  we  are  indebted  to  this  system  of  names,  which  it 
seemed  at  first  so  difficult  to  learn!  Nitrate  of  ammonia  must  be  a  salt  com- 
posed of  nitric  acid  and  ammonia,  or  the  volatile  alkali.  As  ammonia  con- 
sists of  hydrogen  and  nitrogen,  and  nitric  acid  of  oxygen  and  nitrogen,  the 
ultimate  components  of  the  salt  must  be  oxygen,  nitrogen,  and  hydro- 
gen(21). 

Mrs  B.  The  crystallized  salt  in  this  phial  is  nitrate  of  ammonia.  It  may 
be  produced  by  causing  gaseous  ammonia  to  pass  into  nitric  acid.  But 
the  usual  way  of  preparing  it  is  to  dilute  nitric  acid  with  three  or  four  parts 
of  water,  and  to  drop  into  this  mixture  lumps  of  carbonate  of  ammonia 
(volatile  smelling  salts).  An  effervescence  will  immediately  ensue,  arising 
from  the  escape  of  carbonic  acid,  which  is  set  free  in  consequence  of  the  com- 
bination of  the  ammonia  with  the  nitric  acid.  When  this  acid  is  saturated, 
the  nitrate  of  ammonia  maybe  obtained  by  evaporating  the  water  with  which 
the  nitric  acid  was  diluted(22).  In  order  to  decompose  this  salt  a  quantity 
of  it  is  put  into  a  retort,  to  which  the  heat  of  a  lamp  is  applied.  This  will 
first  cause  it  to  fuse,  and  drive  off  a  quantity  of  watery  vapour.  The  fused 
salt  will  presently  boil  up  in  large  distinct  bubbles,  and  the  whole  of  it  will 
gradually  be  converted  into  nitrous  oxide  and  watery  vapour.  The  gas  may 
be  collected  over  water  in  the  usual  way(23). 

Caroline.  I  thought  that  the  watery  vapour  was  to  be  driven  off  before 
the  gas  was  produced;  but  you  now  speak  of  it  as  accompanying  it  through 
the  whole  process. 

Mrs  B.  And  so  it  does.  For  although  you  drive  off  the  water  origi- 
nally contained  in  the  salt,  fresh  portions  of  it  are  formed  during  the  whole 


18.  What  is  said  respecting  hyponitrous  acid? 

19.  By  whom  was  nitrous  oxide  discovered? 

20.  By  what  process  was  it  at  first  obtained? 

21.  What  is  the  composition  of  the  salt  which  affords  it  in  a  pure  state? 

22.  In  what  way  may  nitrate  of  ammonia  be  formed? 

23.  How  is  this  salt  decomposed  to  produce  the  nitrous  oxide  gas? 


ON  THE  PROTOXIDE  OF  NITROGEN.  225 

period  of  the  decomposition.    And  a  little  reflection  will,  I  am  sure,  enable 
you  to  discover  its  source(24). 

Caroline.  I  think  I  perceive  it  now.  The  hydrogen  of  the  ammonia 
must  combine  with  a  portion  of  the  oxygen  of  the  nitric  acid,  and  thus  pro- 
duce water  from  its  elements(25). 

Mrs  JB.  I  was  certain  that  you  would  discover  this  fact;  and  you  must 
likewise  perceive  that  this  union  of  the  hydrogen  of  the  ammonia  with  a  part 
of  the  oxygen  of  the  acid,  must  produce  the  decomposition  of  both  the  consti- 
tuents of  the  nitrate  of  ammonia.  The  atomic  theory  will  aid  you  in  tracing 
out  these  decompositions,  as  it  will  every  other  to  which  you  are  capable  of 
applying  it.  The  nitrate  of  ammonia  consists  of  one  atom  of  ammonia 
united  to  one  atom  of  nitric  acid.  Ammonia  is  formed  by  the  union  of  one 
atom  of  nitrogen  and  three  atoms  of  hydrogen;  and  nitric  acid  of  one  atom 
of  nitrogen  and  five  of  oxygen.  What  are  the  atoms,  therefore,  which  enter 
into  the  composition  of  the  nitrate  of  ammonia? 

Emily.  That  is  very  easily  calculated.  There  are  three  atoms  of  hydro- 
gen, which  are  all  supplied  by  the  ammonia;  two  atoms  of  nitrogen,  one  from 
the  ammonia,  and  the  other  from  the  acid;  and  five  atoms  of  oxygen  derived 
from  the  acid(2fi). 

Jlfrs  B.  Certainly;  and  what  will  be  the  consequence  should  the  three 
atoms  of  hydrogen  combine  with  three  of  oxygen,  and,  by  this  combination, 
form  three  atoms  of  water? 

Emily.  It  is  very  plain  that  two  atoms  of  oxygen  and  two  of  nitrogen 
will  be  left. 

Caroline.  And  it  is  equally  plain  that  these  are  the  elements  of  the  pro- 
toxide of  nitrogen,  or  nitrous  oxide,  which  consists  of  oxygen  and  nitrogen, 
united  atom  to  atom.  And,  as  in  the  decomposition  of  the  salt,  they  are 
presented  to  each  other  in  their  nascent  state,  they  of  course  combine  and 
produce  the  gas  in  question.  How  curious,  how  admirable,  and  how  satisfac- 
tory, are  these  investigations!  How  well  they  repay  the  trouble  of  a 
thorough  examination(27) ! 

Jlfrs  B.  Nitrous  oxide  differs  very  materially  from  nitrous  air.  It  is 
very  readily  absorbed  by  water,  which  takes  up  its  own  bulk  of  this  gas.  A 
taper  will  burn  in  it  more  brilliantly  than  in  atmospheric  air,  and  iron  wire 
undergoes  combustion  in  it  very  brilliantly.  Sulphur  is  extinguished  by  it,  if 
it  is  introduced  whilst  burning  with  a  feeble  blue  flame;  but  if  well  ignited 
with  a  white  flame,  its  combustion  will  be  rendered  more  vivid(28).  If 
oxygen  be  mixed  with  it,  no  new  combination  takes  place,  as  is  the  case  with 
nitric  oxide. 

This  gas  is  not  only  respirable,  but  is  a  very  powerful  stimulant,  pro- 
ducing extraordinary  effects  upon  the  system. 

Emily.  I  have  never  witnessed  the  breathing  of  it,  nor  have  I  any  idea 
how  this  is  managed.  For  myself,  I  confess  that  I  should  be  unwilling  to 
inhale  it,  if  the  accounts  which  I  have  heard  of  its  effects  have  been  correctly 
given. 

Mrs  B.  In  order  to  its  being  breathed,  it  is  first  passed  into  an  oiled  silk 
bag,  or  into  a  bladder,  in  the  way  you  have  witnessed  (p.  133).  A  tube 
attached  to  the  bag  is  held  in  the  mouth,  and  through  this  the  gas  is  breathed 
from  and  into  it.  I  have  frequently  witnessed  its  effects.  Sometimes  it  pro- 
duces the  most  extatic  pleasure;  which  is  evinced  by  leaping,  dancing,  shout- 


24.  What  besides  this  gas  is  produced  in  its  decomposition? 

25.  How  is  the  fact  of  this  production  of  water  explained? 

26.  What  is  the  atomic  composition  of  nitrate  of  ammonia? 

27.  By  what  new  combination  of  these  are  water  and  nitrous  oxide  pro- 
duced ? 

28.  In  what  way  does  this  gas  operate  upon  burning  bodies? 


226 


CONVERSATIONS  ON  CHEMISTRY. 


ing,  and  the  performance  of  antic  gestures  of  almost  every  kind.  Those 
under  its  influence  frequently  manifest  uncommon  strength,  and  if  resisted 
fight  with  great  fury.  In  some  persons  it  totally  destroys  the  muscular 
powers,  and  even  induces  fainting.  In  fact,  its  effects  are  extremely  discor- 
dant, and  though  curious,  are  upon  the  whole,  rather  painful  tovwitness(29). 
Caroline.  Its  influence  very  soon  passes  off,  does  it  not? 
Mrs  B  Yes,  generally  in  the  course  of  two  or  three  minutes,  but  many 
experience  a  degree  of  elasticity  and  cheerfulness  for  hours  after  its  direct 
effect  has  ceased.  I  have  never  known,  or  heard,  of  any  permanently  bad  effect 
from  it,  but  as  there  is  no  advantage  to  result,  I  think  it  best  not  to  try 
it(30). 

Caroline.  I,  for  one,  have  no  inclination  to  get  scientifically  tipsy,  as  I 
well  know,  that  when  in  my  sober  senses,  my  sayings  and  doings  partake 
sufficiently  of  the  extravagant;  and  I  should  expect,  under  the  influence  of 
your  leaping,  dancing  and  shouting  gas,  to  exhibit  the  very  perfection  of  the 
ridiculous. 

Mrs  B.  At  the  commencement  of  our  last  conversation  I  gave  you  a 
table  of  the  combining  atoms  in  the  five  compounds  which  we  have  since 
considered,  and  will  now  present  the  same  to  you,  with  some  additions,  in 
order  that  you  may  investigate  it  at  your  leisure.  In  the  former  table  you 
had  the  number  of  combining  atoms  only;  the  additions  in  the  present  consist 
of  the  atomic  weights  of  the  oxygen  and  nitrogen,  and  of  the  numbers  which 
represent  the  weight  of  an  atom  of  each  of  the  compounds. 


Compounds. 

Atoms  of 
Nitrogen. 

Atomic 
•weight 

Atoms  of 
oxygen. 

Atomic 
•weight. 

Wt.  of  atom 
of  compound. 

1.  Nitrous  oxide 

I 

14 

1 

8 

22 

2.   Nitric  oxide 

1        * 

14 

2 

16 

30 

3.    Hyponitrous  acid 

1 

14 

3 

24 

38 

4.  Nitrous  acid 

1 

14 

4 

32 

46 

5.   Nitric  acid 

1 

14 

5 

40 

54 

Caroline.  I  plainly  perceive  the  use  of  this  table.  It  shows  that  as  an 
atom  of  nitrogen  'is  represented  by  the  number  fourteen,  and  an  atom  of 
oxygen  by  the  number  eight,  if  one  of  each  of  these  combine,  an  atom  of 
the  compound  must  weigh  twenty-two;  whilst  if  the  atom  of  nitrogen  com- 
bines with  two  atoms  of  oxygen,  the  weight  of  the  compound  atom  will  be 
thirty;  as  to  the  twenty-two  must  be  added  the  eight  which  represents  the 
additional  atom  of  oxygen:  and  so  of  the  other  compounds(31). 

Mrs  B.  I  am  gratified  at  your  ready  comprehension  of  the  use  of  this 
table.  It  is  the  practice  now  to  employ  numbers  upon  this  principle,  in 
order  to  represent  all  the  compounds,  the  constitution  of  which  are  known. 
The  numbers  usually  employed  relate  to  hydrogen,  the  atomic  weight  of 
which  being  considered  as  unity.  Thus,  as  you  will  recollect,  an  atom  of 
nitrogen  is  fourteen  times  as  heavy  as  one  of  hydrogen;  an  atom  of  oxygen 
eight  times  as  heavy;  and  therefore  an  atom  of  nitric  acid,  which  consists 
of  one  of  nitrogen  and  five  of  oxygen,  must  be  fifty-four,  times  as  heavy. 
Such  numbers  are  called  equivalents,  and  tables  of  them  accompany  all  the 
modern  treatises  on  chemistry(32). 

Emily.  Such  tables  must  be  not  only  very  useful,  but  I  should  suppose 
absolutely  necessary,  as  it  would  be  scarcely  possible  to  treasure  in  the 


29,  What  is  said  of  the  respiration  of  nitrous  oxide? 

SO.  Is  its  effect  upon  the  system  of  long  continuance? 

81.  What  does  the  above  table  show  respecting  these  compounds? 

32.  What  further  is  said  on  the  subject  of  atomic  weights? 


ON  NITRATE  OF  POTASSA.  227 

memory  all  the  numbers  which  represent  the  atomic  weights,  even  of  the 
simple  substances  alone. 

jifrs  B.  We  have  already  noticed  some  of  the  salts  produced  by  the 
union  of  nitric  acid  with  different  bases,  but  there  is  one  of  them  which  is 
of  such  special  importance,  both  in  chemistry  and  the  arts,  as  to  demand  a 
more  particular  examination  than  either  of  the  others.  I  allude  to  the 
nitrate  ofpotassa. 

NITRATE  OF  POTASSA,  called  also  NITRE  or  SAI.T-PETRE,  was  known  to  the 
Romans.  But  the  earliest  account  which  we  have  of  it  is  derived  from  the 
annals  of  the  Chinese,  who  appear  to  have  been  acquainted  with  it  from 
remote  antiquity.  This  is  the  less  remarkable,  as  it  is  a  natural  product,  and 
is  found  in  many  situations(33).  In  Italy,  Spain,  India,  China,  Persia,  and 
some  other  countries,  it  is  contained  in  the  soil  in  such  large  quantities,  that 
the  greater  part  of  what  is  used  in  Europe  and  in  this  country  is  supplied 
from  those  sources. 

Caroline.  And  has  it  not  been  found  in  the  United  States  also?  I  cer- 
tainly think  that  I  have  read  some  accounts  of  nitre  caves  in  Virginia,  Ken- 
tucky, and  elsewhere. 

Jlfrs  B.  You  are  correct  on  this  point.  There  are  many  nitre  caves, 
as  they  are  called,  from  the  contents  of  which  much  nitre  has  been  manu- 
factured; and  when  the  country  in  their  vicinity  becomes  more  populous,, 
these  caves  may  be  of  great  value(34).  They  contain  a  portion  of  nitrate  of 
potassa,  but  the  predominant  substance  is  nitrate  of  lime,  which,  to  be  convert- 
ed into  nitre,  must  be  decomposed  by  means  of  carbonate  of  potassa.  By  a 
recurrence  to  what  you  have  learnt  respecting  double  elective  attraction, 
(p.  208,)  you  will  readily  understand  this  process.  The  nitrate  of  lime, 
and  the  carbonate  of  potash,  are  both  soluble  in  water,  and  they  can,  there- 
fore, be  mixed  intimately  togWher(35). 

Emily.  And  there  can  be  no  difficulty  in  tracing  their  action  upon  each 
other.  The  nitric  acid  will  displace  the  carbonic  acid  from  the  potash, 
and,  uniting  with  it,  will  form  nitrate  of  potash;  whilst  the  carbonic  acid 
will  combine  with  the  lime,  and  convert  it  into  a  carbonate.  But  how  can 
these  two  new  compounds  be  separated? 

J\frs  B.  They  separate  themselves.  The  nitrate  of  potassa  remains 
in  solution,  whilst  the  carbonate  of  lime,  being  insoluble,  is  precipitated. 
The  nitre  is  afterwards  obtained  in  crystals  by  evaporating  the  water(36). 

The  sweepings  from  the  streets  of  cities,  mixed  with  the  mortar  and  other 
rubbish  from  old  buildings;  the  cleanings  of  cellars,  and  the  earth  from  the 
places  where  cattle  are  numerous,  if  placed  in  heaps,  and  exposed  for  some 
weeks  to  the  action  of  the  atmosphere,  will,  by  this  means,  be  made  to 
afford  nitrate  of  lime  and  of  potassa.  Nearly  the  whole  of  the  nitre  used 
in  France  during  the  wars  of  her  revolution  was  obtained  from  such 
sourees(37). 

Caroline.  Nitre,  I  know,  is  a  very  combustible  substance,  as  I  have 
often  thrown  pieces  of  it  into  the  fire  to  see  the  brilliancy  with  which  it 
would  burn.  This,  however,  I  do  not  understand,  as  it  is  composed  of  nitric 
acid  and  potash,  neither  of  which  is  combustible  alone(38). 

J\frs  B.  Nor  are  they  so  when  in  combination;  when  you  have  thrown 
nitre  into  the  fire,  you  have  allowed  your  senses  to  deceive  you.  '  The  nitre 


33.  What  is  observed  respecting  the  natural  production  of  mire? 
,34.  From  what  places  has  it  been  principally  obtained  ? 

35.  What  is  observed  of  the  nitre  caves  of  the  United  States? 

36.  How  is  nitrate  of  time  converted  into  nitrate  ofpotassa? 

37.  How  may  nitre  be  artificially  produced  ? 

38.  What  does  Caroline  observe  respecting  the  combustion  of  nitre? 


228  CONVERSATIONS  ON  CHEMISTRY. 

merely  imparted  oxygen  to  the  coals,  and  caused  them  to  hum  brilliantly^ 
Had  you  thrown  your  nitre  upon  a  brick  or  stone,  heated  to  redness,  there 
would  not  have  been  any  appearance  of  combustion(39). 

Caroline,  I  plainly  perceive  my  error,  now  you  have  pointed  to  its 
source.  There  was  no  fact,  however,  which  I  considered  as  more  completely 
established  than  that  of  the  combustibility  of  nitre. 

Mrs  B.  Your  mistake  was  a  very  natural,  and  a  very  common  one;  as 
the  appearance  to  which  you  alluded  seems  .fully  to  justify  the  inference 
drawn  from  it. 

Nitre,  when  brought  to  a  low  red  heat,  is  decomposed,  affording,  in  the  first 
instance,  a  large  quantity  of  oxygen  gas,  sufficiently  pure  for  all  the  ordinary 
experiments  of  the  laboratory,  or  of  the  lecture  room.  To  obtain  the  gas 
from  this  salt,  a  portion  of  it  is  put  into  a  retort  of  iron  or  of  earthenware, 
to  which  a  long  tube  is  attached,  in  order  to  conduct  the  oxygen  into  a  re- 
ceiver; the  retort  is  placed  in  a  fire,  and  as  soon  as  it  becomes  red-hot,  the 
extrication  of  the  gas  commences.  One  pound  of  nitre  will  yield  about 
seven  gallons  of  oxygen.  If,  however,  the  process  be  continued  too  long, 
or  the  heat  be  too  great,  a  portion  of  nitrogen  will  accompany  the  oxygen, 
and  at  length  nitrogen  nearly  pure  will  pass  over,  and  the  process  be 
defeated(40). 

Emily.  lam  not  surprised  that  oxygen  and  nitrogen  are  both  extricated 
from  nitre,  as  the  nitric  acid  is  so  readily  decomposed  by  heat;  but  why 
they  should  not  be  mixed  together  during  the  whole  process  I  do  not  com- 
prehend. 

Mrs  B.  During  the  first  period  of  the  decomposition,  oxygen  alone  is  ob- 
tained, because  the  nitric  is  merely  reduced  to  the  state  of  nitrous  acid,  Avhilst 
this  last  is  retained  by  the  attraction  of  the  potash,  forming  with  it  a  nitrite  of 
potash;\)ui  if  the  decomposition  be  pushed  further,  this  nitrous  acid  will  also 
be  decomposed,  and  nitric  oxide  and  nitrogen  gases  will  be  obtained  instead 
of  oxygen(4l). 

You  now  understand  that  the  reason  why  nitre  pro- 
motes combustion,  is  the  facility  with  which  it  parts  Earthen  Crucible*. 
with  its  oxygen.  The  metals  are  sometimes  oxidized 
by  what  is  called  DEFLAGRATION.  That  is,  by  mixing 
them  with  nitre,  and  projecting  the  mixture  into  a  red 
hot  crucible.  The  nitre  is  thus  made  to  yield  its  oxygen 
to  the  metal(42). 

Caroline.  Crucibles,  I  believe,  are  earthen  vessels 
in  which  metals  are  melted,  and  other  substances  heated 
in  the  fire. 

Mrs  B.  The  chemist  sometimes  uses  crucicles  of  platinum,  or  of  silver. 
But  for  most  purposes  they  are  made  of  earthenware(43).  I  have  two  of 
these  latter  now  in  the  fire,  and  heated  to  redness.  In  one  of  them  I  will 
show  you  the  deflagration  of  charcoal,  and  that  of  sulphur  in  the  other.  For 
this  purpose  I  have  pulverized  portions  of  each  of  these  substances,  and 
mixed  them  separately  with  nitre.  Into  this  crucible  I  throw  some  of  thu 
mixture  of  sulphur  and  nitre. 

Emily.  That  is  really  a  rapid  and  beautiful  combustion.  The  sulphut 
burns  more  splendidly  than  it  did  in  oxygen  gas,  in  your  experiment  some 
time  ago.  It  is  well  that  the  vapour  passes  up  the  chimney,  for  even  now  it 
gives  out  a  strong  smell  of  sulphurous  acid. 


39.  What  appears  to  be  the  fact  upon  this  subject? 

40.  In  what  way  may  oxygen  gas  be  obtained  from  nitre? 

41.  What  further  remarks  are  made  on  the  decomposition  of  this  salt? 

42.  What  is  deflagration,  and  how  is  it  effected? 
^  43.  What  are  crucibles? 


ON  DEFLAGRATION  AND  DETONATION.  229 

Mrs  B.  Both  sulphurous  and  sulphuric  acids  are  produced  in  this  process, 
and  a  portion  of  the  latter  combines  with  the  potash  of  the  nitre,  forming  a 
sulphate  of  potash,  which  will  remain  in  the  crucible;  sulphurous  acid  and 
nitrogen  passing  off  in  the  gaseous  state(44). 

I  will  now  deflagrate  the  charcoal  in  the  other  crucible. 

Caroline.     It  burns  almost  like  gunpowder,  only  more  slowly. 

Mrs  B.  If  we  had  mixed  the  three  together,  that  is,  the  charcoal,  sul- 
phur and  nitre,  they  would  have  burnt  exactly  like  gunpowder,  for  such 
they  would  actually  have  been(45).  And  instead  of  a  deflagration,  we 
should  have  had  a  DETONATION;  that  is  a  combustion  so  rapid  as  to  produce 
an  explosion  accompanied  with  a  loud  report(46). 

Gunpowder  is  made  by  combining  together,  very  intimately,  six  parts  of 
nitre,  one  of  charcoal,  and  one  of  sulphur,  and  you  are  aware  of  the  rapi- 
dity with  which  this  mixture  burns,  and  of  the  immense  force  with  which  it 
explodes(47). 

Emily.     And  how  is  this  violent  detonation  of  gunpowder  accounted  for? 

Mrs  B.  When  we  deflagrated  the  sulphur,  sulphurous  acid  and  nitrogen 
gases  escaped,  and  from  the  deflagrated  charcoal  carbonic  acid  was  produced, 
which  was  also  accompanied  by  the  nitrogen  of  the  decomposed  nitric  acid. 
With  the  exception  of  the  potash,  nearly  the  whole  of  the  solid  powder, 
therefore,  suddenly  assumes  the  gaseous  form.  This  gaseous  matter,  from 
its  quantity  and  from  its  expansion  by  the  high  degree  of  heat  produced  by  the 
combustion,  operates  with  a  force  about  one  thousand  times  greater  than  that  of 
the  atmosphere.  And  it  is  this  expansion  which  produces  the  detonation(48). 

Caroline.  The  heat  accompanying  this  and  similar  explosions  occasioned 
by  the  rapid  formation  of  gaseous  matter,  you  adduced  as  one  of  the  objec- 
tions against  the  Lavoisierian  theory  of  combustion,  and  it  certainly  is  a  valid 
one,  as  according  to  that  theory,  the  sudden  formation  of  gaseous  matter  by 
the  dilatation  of  solids  ought  to  produce  cold.  Yet  in  this  case  and  many 
others,  heat  is  disengaged(49). 

Mrs  B.  An  explosive  mixture  called  pulvis  fulminans,  or  fulminating 
powder,  is  made  by  mixing  together  in  a  mortar,  three  parts  of  nitre,  two 
of  pearl  ashes  (carbonate  of  potash),  and  one  of  sulphur.  A  few  grains 
of  this  powder  placed  in  a  spoon  and  held  over  a  lamp  until  it  melts,  will 
explode  with  a  very  loud  report.  This  explosion,  like  that  of  gunpowder, 
is  occasioned  by  the  sudden  formation  of  gases(SO). 

Nitre  is  one  of  the  most  useful  of  the  saline  compounds.  Its  greatest 
consumption  is  in  the  manufacture  of  gunpowder;  but  it  is  employed  for  many 
purposes  in  the  laboratory  of  the  chemist,  to  whom  it  affords  oxygen,  and 
nitric  acid,  and  aids  in  the  formation  of  sulphuric  acid.  The  refiner  of 
metals  uses  it  in  his  operations;  the  physician  administers  it  in  small  doses  to 
allay  fever,  and  by  fumigating  infected  places  by  the  vapour  of  nitrous  acid, 
disengaged  from  this  salt,  it  is  said  that  the  matter  of,  contagion  has  been 
destroyed.  Its  application  to  the  salting  of  meat  is  familiarly  known(51). 

Emily.  I  am  apprehensive  that  after  nitrate  of  potash,  the  other  suits  of 
this  class  will  appear  comparatively  insignificant. 

Mrs  B.  Some  of  them,  such  as  the  nitrate  of  silver,  and  the  nitrates  of 
some  other  metals,  have  been  already  noticed.  The  nitrate  of  lime  is  prin- 


44.  What  is  formed  by  the  deflagration  of  sulphur? 

45.  Of  what  ingredients  does  gunpowder  consist? 

46.  What  is  meant  by  detonation? 

47.  In  what  proportions  are  the  ingredients  of  gunpowder  mixed? 

48.  How  is  the  violent  detonation  of  gunpowder  accounted  for? 

49.  Does  the  Lavoisierian  theory  of  combustion  explain  this  phenomenon? 

50.  How  is  fulminating  powder  formed? 

51.  Detail  some  of  the  uses  to  which  nitre  is  applied. 

U 


230  CONVERSATIONS  ON  CHEMISTRY. 

cipally  valuable  as  affording  nitre.  The  nitrate  of  ammonia  you  have  seen 
produced,  and  decomposed  for  the  purpose  of  making  nitrous  oxide.  Nitrate 
of  soda  is  in  many  respects  similar  to  nitre;  but  in  utility  it  is  very  inferior  to 
it.  The  nitrates  possess  one  property  in  common;  that  is,  the  facility  with 
which  they  afford  oxygen  to  most  combustibles.  They  have  hence  been 
classed  by  some  chemists  among  what  they  have  denominated  compound  sup" 
porters  of  combustion(52).  With  the  exhibition  of  an  experiment  by  means 
of  nitrate  of  copper  and  tin  foil,  I  shall  dismiss  this  class  of  bodies. 

Caroline.  This  green  salt,  labelled  nitrate  of  copper,  you  obtained,  I 
believe,  by  evaporating  the  liquid  nitrate  which  was  formed  when  you  pro- 
cured the  nitric  oxide,  or  nitrous  air. 

Mrs  B.  It  is  the  same.  I  take  some  of  this  crystallized  nitrate,  dry  and  in 
powder,  and  wrap  it  up  in  a  piece  of  tin  foil.  The  two  materials  will  not, 
under  these  circumstances,  act  sensibly  upon  each  other.  I  now  take  another 
piece  of  foil,  and  a  quantity  of  the  pulverized  nitrate  as  before.  Upon  this  I 
sprinkle  a  few  drops  of  water,  and  quickly  wrap  it  up  in  the  foil,  just  as  I 
did  in  the  former  case. 

Emily.  It  has  burnt,  and  actually  emits  sparks  of  fire,  whilst  that  which 
was  dry  still  remains  unchanged(53). 

Mrs  B.  The  water  serves  to  dissolve  a  portion  of  the  nitrate  of  copper, 
and  thus  to  bring  it  into  close  contact  with  the  tin.  This  metal  having  a 
strong  affinity  for  oxygen,  decomposes  the  nitric  acid  of  the  nitrate  of 
copper,  and  combines  with  its  oxygen  with  such  rapidity  as  to  undergo 
combustion(54). 

When  we  next  meet,  several  different  subjects  will  engage  our  attention: 
muriatic  acid  and  chlorine,  however,  will  be  the  principal. 


CONVERSATION  XXIII. 

ON  CYANOGEN,  SELENIUM,  BORON,  FLUORIC  ACID,  MURIATIC 
ACID,  AND  CHLORINE. 

Cyanogen,  or  Bicarburet  of  Nitrogen.  Hydrocyanic,  or  Pru&sic  Acid. 
Hydrogen,  an  acidifying  principle.  Hydracids.  Prussian  Blue.  Prussia 
Acid  in  Vegetables.  Cyanic  Add.  Selenium.  Boracic  Acid.  Borate  of 
Soda,  or  Borax.  Boron.  Fluoric  Acid.  Fluate  of  Lime,  or  Derbyshire 
Spar.  Silex  and  Glass  dissolved  by  Fluoric  acid.  Etching  upon  Glass. 
Fluo-silicic  Acid  Gas.  Fluorine,  the  unkno-wn  Base  of  Fluoric  Acid. 
Muriatic  Acid,  or  Spirit  of  Sea  Salt.  First  procured  in  its  Gaseous  Form  by 
Priestley.  Obtained  from  Muriate  of  Soda.  Description  of  Woulfe's 
Apparatus.  Oxy^muriatic  Acid,  or  Chlorine.  Combustion  of  Metals,  and 
of  Phosphorus  in  this  Gas.  Its  Bleaching  Properties.  Theory  of  its  pro- 
duction.  Two  Theories  respecting  its  Nature.  Proofs  that  it  does  not 
contain  Oxygen.  Effect  of  Light  upon  a  Mixture  of  Gaseous  Chlorine  and 
Hydrogen.  Common  mode  of  obtaining  Chlorine. 

Mrs  B.  In  our  last  conversation,  we  have  seen  nitrogen,  when  in  com- 
bination with  oxygen,  exhibiting  very  active  properties.  You  had  previously 
witnessed  a  similar  fact,  when  examining  4he  volatile  alkali,  in  which  nitro- 


52.  What  is  observed  respecting  the  nitrates  generally? 

53.  Describe  the  experiment  with  nitrate  of  copper  and  tin  foil? 

54.  What  appears  to  be  the  agency  of  the  water  in  this  case? 


ON  CYANOGEN  AND  PRUSSIC  ACID.  231 

gen  united  with  hydrogen  became  a  chemical  agent  of  great  power.  I  am 
now  about  to  introduce  it  to  you  under  a  new  character,  resulting  from  its 
alliance  to  carbon,  with  which  it  forms  a  gas,  sometimes  called  the  bicar- 
buret  of  nitrogen,  but  more  generally  denominated  CYANOGEN.  The  first 
name  may  serve  to  indicate  its  composition,  the  last,  one  of  its  particular 
properties,  as  it  is  derived  from  two  Greek  words,  signifying  blue,  and  to 
produce;  cyanogen  producing  a  blue  colour  by  its  combination  with  oxide 
of  iron,  as  is  seen  in  that  beautiful  pigment  Prussian  blue(l). 

Caroline.  This  paint  then  is  a  compound  of  oxide  of  iron,  nitrogen,  and 
carbon.  I  should  never  have  supposed  that  it  was  so  complex  an  article. 

Mrs  B.  It  is  more  complex  than  you  even  yet  suppose;  as  the  cyanogen, 
before  it  combines  with  the  oxide  of  iron,  is  itself  converted  into  an  acid, 
called  HYDROCTANTC,  or  PH.USSIC  ACID.  This  acid  claims  your  particular 
attention,  as  hydrogen  is  its  acidifying  principle(2).  There  are  several 
other  acids  in  which  hydrogen  performs  the  office  once  supposed  to  belong 
exclusively  to  oxygen.  This  was  intimated  when  speaking  of  sulphuretted 
hydrogen  (p.  141).  Acids  of  this  kind  are  called  hydracids.  The  name 
hydrocyanic,  applied  to  prussic  acid,  serves  to  point  it  out  as  a  compound 
of  hydrogen  and  cyanogen(S). 

Emily.  The  name  prussic  acid  is  evidently  derived  from  that  of  the 
colour  which  contains  it.  And  although  not  so  systematic  as  hydrocyanic, 
it  seems  to  be  more  convenient,  as  showing  its  origin. 

Mrs  B.  Both  names  are  used,  and  1  shall  employ  them  indiscriminately, 
that  they  may  become  equally  familiar  to  you(4). 

To  obtain  cyanogen,  a  prussiate  ofmercuryis  formed  by  boiling  Prussian 
blue  (hydrocyanate  of  iron)  with  red  oxide  of  mercury;  the  prussiate  of 
mercury  thus  formed  is  decomposed  by  heat,  and  affords  cyanogen.  It  is  a 
colourless  gas  of  a  very  pungent  odour,  and,  like  hydrogen,  extinguishes 
burning  bodies,  whilst  it  is  itself  inflammable(5).  When  combined  with 
hydrogen,  under  the  form  of  prussic  acid,  it  furnishes  one  of  *.he  most  active 
and  virulent  poisons  with  which  we  are  acquainted.  A  single  drop  of  it 
placed  on  the  tongue  of  a  large  dog  caused  his  death  in  the  course  of  a 
few  seconds.  The  vapour  which  rises  from  it,  and  mixes  with  the  atmos- 
phere during  its  preparation,  produces  headach,  giddiness,  and  fainting(6)» 

Caroline.  I  shall  take  good  care  to  avoid  the  contact  of  so  dangerous  a 
compound;  and  shall  almost  fear  to  paint  again  with  Prussian  blue. 

Mrs  B.  Your  fear  will  be  groundless,  and  your  caution  unavailing.  In 
Prussian  blue  the  acid  is  disarmed  of  its  terrors  by  its  combination  with 
iron.  But  it  exists  in  a  free  state  in  the  liqueur  called  noyeau,  the  peculiar 
odour  and  flavour  of  which  are  produced  by  it.  Bitter  almonds,  and  the 
kernels  of  peaches,  cherries,  and  other  fruits  contain  it.  You  are  not  likely 
therefore  always  to  avoid  contact  with  it,  or  if  you  do,  you  must  not  only  be 
very  cautious  but  very  self-denying.  The  extremely  poisonous  water  distilled 
from  the  cherry  laurel  (prunus  lauro-cerasusj  derives  its  qualities  from 
the  large  quantity  of  this  acid  which  it  contains.  Prussie  acid  has  been  in- 
troduced into  medicine;  and  you  are  aware  that  such  is  the  case  with  other 
active  poisons,  and  that  they  hold  a  place  among  the  most  valuable  of  our 
remedies(7).  :YT" 

Emily.    Are  there  many  important  salts  formed  by  the  hydrocyanic  acid? 


1.  Of  what  is  cyanogen  composed,  and  what  does  it  form  with  oxide  of 
iron? 

2.  What  is  prussic  acid,  and  how  is  it  formed? 

3.  What  is  remarked  respecting  some  analogous  acids? 

4.  What  is  observed  respecting  the  two  names  of  prussic  acid?         - 

5.  From  what  is  cyanogen  obtained,  and  in  what  form  does  it  exist? 

6.  What  is  said  of  hydrocyanic,  or  prussic  acid,  as  a  poison? 

7.  Of  what  vegetables  does  it  form  a  component  part? 


232  CONVERSATIONS  ON  CHEMISTRY. 

J\frs  B.  The  ferrocyanate  or  prussiate  of  iron  is  the  principal.  Com- 
bined with  potash,  it  forms  prussiate  of  potash,  which  is  used  as  a  test  of  the 
presence  of  iron,  to  the  solutions  of  which  it  imparts  a  fine  blue  colour. 
Cyanogen  forms  an  acid,  not  only  by  its  combination  with  hydrogen,  but  also 
by  combining  with  oxygen.  This  latter  is  called  cyanic  acid,  but  its  pro- 
perties, or  those  of  its  combinations,  do  not  require  our  notice(8).  I  shall 
therefore  dismiss  cyanogen,  and  direct  your  attention  fora  few  minutes  to  a 
substance  called  selenium. 

Emily.  This,  I  believe,  is  as  new  to  us  as  cyanogen.  I  do  not  recollect 
that  we  have  ever  heard  you  name  it  until  now. 

J\frs  B.  SELENIUM  is  a  peculiar  substance,  apparently  simple,  which  has 
been  discovered,  in  company  with  sulphur,  in  some  sulphurets  of  iron,  and 
in  a  few  other  combinations.  The  quantity  of  it  which  has  been  obtained 
is  very  small.  Its  appearance  is  somewhat  metallic,  and  from  this  cause  it  was 
at  first  classed  with  the  metals;  but  it  is  now  considered  as  more  nearly  allied 
to  suiphur(9).  It  is  combustible,  although  it  burns  witb  difficulty.  Its 
vapour  has  a  very  peculiar  odour,  resembling  that  of  decayed  horse-radish 
It  combines  with  oxygen  in  three  proportions,  forming  oxide  of  selenium, 
and  selenious  and  selenic  acids(lQ').  We  know  but  little  more  respecting  it, 
and  shall  therefore  pass  on  to  other  matters. 

Caroline.  I  am  at  a  loss  to  perceive  what  useful  purpose  can  be  an- 
swered in  the  economy  of  nature  by  substances  so  sparingly  diffused  as 
selenium,  yttria,  and  some  others. 

Jlfrs  B.  This  is  a  point  upon  which  your  curiosity  is  likely  to  remain 
unsatisfied,  as  those  who  are  wiser  than  we  can  pretend  to  be,  are  obliged, 
on  this  subject,  to  rest  satisfied  with  the  assurance,  that  the  Being  who 
created  these  materials,  acted,  in  their  creation,  under  the  guidance  of  that 
wisdom  which  is  distinctly  manifested  in  all  his  works,  so  far  as  human 
power  can  investigate  them. 

Emily.  The  phial  from  which  you  have  just  poured  these  shining  crys- 
talline scales  is  labelled  BOKACIC  ACID  ;  this  differs  essentially  from  most 
of  the  acids  that  we  have  lately  seen. 

Caroline.  After  such  articles  as  sulphuric,  nitric,  and  especially  prus- 
sic  acid,  to  which  we  have  been  lately  introduced,  I  am  glad  to  meet  with 
one  that  we  need  not  fear  to  touch,  and  which  appears  to  be  perfectly 
innocent. 

Mrs  B.  BORACIC  ACID  is  obtained  from  a  salt  usually  called  borax, 
the  borate  of  soda  of  the  chemist3(ll).  The  borate  of  soda  is  used  in 
soldering,  in  refining  metals,  and  in  some  other  processes  in  the  arts. 
This  native  alkaline  salt  is  found  in  large  quantities  in  the  East  Indies, 
•where  there  are  several  lakes  in  the  bottoms  of  which  it  is  constantly  de- 
posited; and  it  is  now  procured  in  considerable  quantities  in  Tuscany.  In 
the  impure  state  in  which  it  is  imported,  it  is  called  tincal;  but  that  which 
you  see  in  this  other  phial  is  refined  borax(12). 

Emily.  This  salt  must,  of  course,  be  decomposed  in  order  to  separate 
the  soda  from  it,  and  thus  to  furnish  the  boracic  acid? 

J\frs  B.  Yes;  and  the  decomposition  is  very  readily  effected  in  conse- 
quence of  the  boracic  acid  being  but  sparingly  soluble  in  water.  The  Borate 
of  soda  is  first  dissolved  in  this  fluid,  and  to  the  solution  is  added  sulphuric 
acid,  which  combines  with  the  soda,  forming  sulphate  of  soda  (Glauber's 
salt)  The  boracic  acid,  from  its  insolubility,  is  precipitated  in  shining 


8.  What  is  said  of  its  salts,  and  of  cyanic  acid? 

9.  What  information  is  given  respecting  selenium? 

10.  What  are  its  properties  and  combinations? 

11.  What  is  the  appearance  of  boracic  acid,  and  from  what  is  it  obtained  > 
A2.  Where  is  borax  procured,  and  to  what  uses  is  it  applied. > 


ON  BORACIC  AND  FLUORIC  ACIDS.  233 

scales,  and  these,  after  pouring  off  the   solution,  are  washed  with  pure 
water,  and  then  dried(l3). 

Caroline.  But  that,  I  suppose,  is  only  a  partial  decomposition,  as  this 
acid,  like  its  relatives,  must  also  be  a  compound. 

Mrs  B.  It  had  long  resisted  every  attempt  to  decompose  it,  hut  at  length 
Sir  Humphry  Davy  succeeded  in  effecting  its  decomposition,  hy  subjecting 
it  to  the  action  of  his  powerful  voltaic  battery:  by  this  means  he  obtained 
from  it  its  base,  which  is  denominated  BOROX.  This  is  an  olive  coloured 
substance,  which  appears  to  be  as  insoluble  and  as  inactive  as  charcoal(l4). 
On  heating  it  in  oxygen  gas,  it  burns  with  considerable  brilliancy,  and  is 
reconverted  into  boracic  acid.  One  characteristic  of  this  acid  is  its  solu- 
bility in  alcohol,  and  its  imparting  to  that  liquid  the  property  of  burning 
with  a  beautiful  green  name,  as  you  will  see  by  that  which  I  inflame  in  this 
spoon. 

Emily.  The  colour  is  certainly  beautiful,  and  quite  peculiar.  This 
combustion  must  offer  an  easy  mode  of  distinguishing  this  acid(15). 

J\frs  B.  Boracic  acid  is  but  sparingly  employed  in  medicine  or  the  arts, 
and  its  combinations,  excepting  that  in  which  it  is  found  in  nature,  offer  no- 
thing of  importance.  I  shall  therefore  proceed  to  the  examination  of  the 
fluoric  acid,  and  some  of  its  salts. 

FLUORIC  ACID  you  will  find  to  be  a  substance  of  much  greater  interest 
than  those  which  we  have  last  examined.  The  beautiful  , vases  which 
stand  as  ornaments  upon  the  mantle  contain  this  acid;  the  substance  of  which 
they  are  formed  being  the  FLUATE  OF  LIME. 

Caroline.  I  have  always  heard  this  kind  of  stone  called  Derbyshire 
spar,  and  recollect  well  the  account  of  the  mines  in  which  it  is  found,  and 
the  manner  of  working  it  into  various  ornaments.  This  spar  is  not  ob- 
tained, I  believe,  in  any  other  place  excepting  Derbyshire  in  England(lG)? 

Mrs  B.  Yes;  it  is  found  in  almost  every  country,  and  sometimes  in 
large  masses,  though  most  commonly  in  thin  veins,  or  small  pieces.  It  is, 
however,  only  in  the  place  you  mention,  that  it  is  met  with  of  a  texture 
•which  admits  of  its  being  wrought  into  ornaments.  This  mineral  is  often 
called  Jluor  spar,  a  name  which  it  derived  from  its  fusibility,  and  from  its 
consequent  use  as  a  jlux  in  the  reduction  of  the  ores  of  some  metals.  The 
acid  which  is  obtained  from  it  is,  as  I  have  already  informed  you,  called  the 
fluoric  aeid(17). 

Emily.  And  what  are  the  peculiar  properties  which  render  this  acid  an 
object  of  particular  interest? 

Mrs  B.  Have  you  forgotten  my  allusion  to  it,  when  speaking  upon 
the  subjnctof  silex?  This  acid  readily  dissolves  flint  and  all  the  other  sili- 
ceous minerals,  and  therefore  cannot  be  obtained,  or  kept,  in  glass  vessels; 
the  silex  and  alkali  of  which  glass  consists  yielding  rapidly  to  its  solvent 
power.  Lead  is  but  slightly,  and  silver  not  at  all,  affected  by  it;  and  there- 
fore, one  or  other  of  these  metals  is  used  in  the  procuring  of,  and  in  ex- 
perimenting with  the  acid(18). 

Fluoric  acid  is  obtained  by  pouring  sulphuric  acid  upon  the  fluor  spar. 
The  sulphuric  acid  combines  with  the  lime  of  the  spar,  converting  it  into  a 
sulphate,  whilst  the  fluoric  acid,  which  is  a  very  volatile  liquid,  distils 
over,  and  is  condensed  in  a  vessel  surrounded  by  ice(19).  Whether  in  the 



13.  By  what  process  is  the  boracic  acid  separated  from  borax? 

14.  What  is  the  base  of  this  acid  called,  and  what  is  its  appearance? 

15.  What  particular  properties  of  boracic  acid  are  mentioned? 

16.  In  what  mineral  is  fluoric  acid  contained?       ;  y  . , 

17.  What  is  said  of  the  names  and  the  localities  of  this  mineral? 

18.  What  are  the  distinguishing  properties  of  fluoric  acid? 
„    19.   How  is  it  separated  from  its  combination  with  lime  ? 

U  2 


234  CONVERSATIONS  ON  CHEMISTRY. 

liquid  form,  or  in  that  of  vapour,  it  is,  next  to  prussic  acid,  the  most  cor- 
rosive and  deleterious  of  all  this  class  of  bodies.  The  vapour  which  escapes 
from  it  excites  violent  fever,  and  produces  long  continued  and  intense  suf- 
fering. A  drop  of  the  liquid  coming  in  contact  with  the  skin  will  form  a 
deep  seated  and  obstinate  ulcer.  A  dog,  upon  whose  back  six  drops  of  it  had 
been  allowed  to  fall,  suffered  extreme  agony,  and  died  in  the  space  of  a  few 
hours(2Cf). 

Caroline.  I  shudder  at  the  very  idea  of  such  a  compound,  and  have  no 
inclination  to  disturb  it  in  its  quiet  possession  of  the  lime  in  the  fluor  spar. 

Mrs  B.  We  can,  with  perfect  safety,  obtain  enough  of  it  to  enable  us 
to  examine  its  effects  in  dissolving,  or  corroding,  glass.  Pictures  are  some- 
times etched  upon  pieces  of  glass  by  means  of  the  liquid  acid.  A  similar 
effect,  however,  may  be  produced,  though  less  perfectly,  by  very  simple 
means.  I  have  prepared  this  small  pane  of 

glass  for  etching,  by  making  it  warm  and  then  Glass  and  trough  for  etch- 
rubbing  bees-wax  upon  it,  so  as  to  coat  it  com-  ing  toiih  Fluoric  Jlcid. 
pletely  over  on  both  sides.  By  means  of  a  sharp 
point,  I  have,  on  one  side,  drawn  a  flower 
through  the  wax  coating,  taking  care  that  the 
point  should  penetrate  to  the  glass.  If  I  now 
expose  that  side  to  the  vapour  of  fluoric  acid, 
the  part  covered  with  wax  will  be  defended 
from  its  action,  whilst  those  which  the  point 
has  made  bare  will  be  engraved,  or  rather 
etched,  having  lines  distinctly  excavated  in  the 
glass.  " 

Emily.     And  how  will  you  manage  to  apply  the  vapour? 

Mrs  B.  I  have  a  tray  made  of  lead,  somewhat  smaller  than  the  glass  to 
be  etched;  into  this  I  put  a  portion  of  the  spar,  in  powder,  and  pour  on  it 
sulphuric  acid  enough  to  moisten  it.  This  tray  I  now  cover  with  the  glass, 
placing  the  drawing  downwards.  The  fluoric  acid,  in  vapour,  will  rise 
from  the  spar,  and  act  upon  the  glass.  To  accelerate  the  operation,  the 
tray  may  be  heated,  but,  of  course,  not  sufficiently  to  melt  the  wax.  The  etch- 
ing may  require  half  an  hour  for  its  completion.  Instead  of  the  leaden 
tray,  I  have  sometimes  used  a  common  saucer  coated  with  bees-wax,  which 
serves  to  protect  it  from  the  acid(21). 

Caroline.  The  compound  formed  by  the  union  of  the  fluoric  acid  with 
the  silex  must  be  a  fluate  of  silica,  that  is,  if  it  is  accounted  a  saline  body. 

Mrs  JB.  Instead  of  forming  a  salt,  it  still  appears  to  possess  the  proper- 
ties of  an  acid;  and,  what  is  very  remarkable,  as  it  forms  this  combination, 
it  passes  into  the  gaseous  form.  The  liquid  fluoric  acid  unites  with  solid 
silex,  and  this  union  produces  an  elastic  fluid,  which  is  called  Jluo-silicic 
acid  gas(<2<2,}. 

Caroline.     No  wonder  that  stones  fall  from  the  atmosphere,  when  flint  \ 
can  be  converted  into  thin  air!     This  is  certainly  one  of  the  most  extraor- 
dinary of  the  gases. 

Mrs  B.  Whilst  kept  from  moisture,  this  gas  is  a  permanently  elastic 
fluid,  but  water  absorbs  it  with  very  gceat  rapidity.  When  this  absorption 
takes  place,  the  gas  deposits  about  one-third  of  the  silex  which  it  contained. 
This  gives  rise  to  a  very  curious  phenomenon.  As  the  separation  takes 
place  on  the  passage  of  the  gas  into  the  water,  the  silex  is  deposited  upon 
its  surface,  where  it  forms  an  incrustation  resembling  a  thin  pane  of  glass, 


20.  Relate  what  is  said  respecting  its  corrosive  properties? 

21.  How  may  glass  be  etdhed  by  means  of  this  acid? 

22.  What  combination  does  fluoric  acid  form  with  silica? 


ON  MURIATIC  ACID.  235 

•which,  unless  it  is  broken,  arrests  the  further  absorption  of  the  gas.  Any 
moist  substance,  if  exposed  to  an  atmosphere  of  this  gas,  will  acquire  an 
incrustation  of  silex;  a  sprig  of  any  vegetable,  or  a  small  animal,  may 
thus  be  made  to  assume  the  appearance  of  a  petrifaction(23). 

Emily,  You  have  not  informed  us,  Mrs  B.,  respecting  the  composition 
of  the  fluoric  acid  itself:  has  it  been  decomposed? 

•Mrs  B.  The  name  Fluorine  has  been  given  to  the  supposed  base  of 
this  acid.  But  although  the  most  able  chemists  have  been  engaged  in  the 
attempt  to  discover  its  composition,  it  has  hitherto  resisted  their  efforts. 
It  is  believed  by  many  to  be  one  of  the  hydracids,  having  a  peculiar  un- 
known base,  acidified  by  its  combination  with  hydrogen.  In  conformity 
with  this  opinion,  it  is  sometimes  called  hydro-fluoric  aczW(24). 

Caroline.  May  there  not  be  such  a  thing  as  a  simple  acid?  If  so,  the 
endeavours  of  the  chemist  to  decompose  it  must,  of  course,  be  altogether 
in  vain. 

•Mrs  B.  The  existence  of  such  an  acid  is,  undoubtedly,  possible;  but 
•where  we  have  not  been  able  to  arrive  at  certainty  in  our  conclusions,  we 
must  adopt  as  our  guides  those  high  probabilities  which  are  the  result  of 
our  reasoning  upon  analogous  facts?  and  strong  analogy  will  not  permit  us 
to  doubt  that  the  fluoric,  like  all  the  other  known  acids,  is  a  compound, 
•A  few  years  since,  there  were  three  acids  classed  together  as  undecouv- 
posed  bodies;  the  boracic,  the  fluoric^  and  the  muriatic.  The  first,  the 
boracic,  has  been  decomposed,  so  as  to  leave  no  doubt  of  its  nature;  the  se- 
cond, the  fluoric,  has  not  yet  yielded  to  the  efforts  of  the  chemist;  the  third, 
the  muriatic,  is  now  admitted  into  the  class  of  hydracids  as  a  compound  of 
chlorine  and  hydrogen(25).  It  is  to  the  properties  of  the  latter  acid  and 
to  its  base  that  I  shall  now  direct  your  attention;  and  it  is  my  design  to 
treat  this  subject  by  the  analytical  method;  first  explaining  to  you  thfi 
properties  of  the  acid,  and  afterwards  inquiring  into  its  composition. 

Emily.  This  seems  to  be  a  very  natural  mode  of  proceeding,  as  it  is 
that  in  which  the  chemist  must  acquire  his  knowledge  in  the  first  instance; 
for  nature  presents  but  very  few  substances  to  him  in  their  simple  or  ele- 
mentary form,  but  furnishes  compounds  which  he  is  compelled  to  analyze. 

Mrs  JB.  MURIATIC  ACID  is  found  in  nature  combined  with  lime,  mag- 
nesia, and  soda;  but  most  abundantly  with  the  last.  The  common  salt  of  our 
tables  is  the  muriate  of  soJa(26),  and  from  this  the  liquid  muriatic  acid  is 
disengaged  by  the  agency  of  sulphuric  acid.  Glauber,  a  Dutch  chemist  of 
the  sixteenth  century,  was  the  first  who  obtained  it  by  this  process;  and  from 
his  name,  the  sulphate  of  soda,  which  remains  in  the  retort  after  the  muriatic 
acid  is  driven  off,  was  called  Glauber's  salt(27). 

As  the  sea  is  the  great  source  of  the  muriate  of  soda,  the  acid  obtained 
from  it  was  called  the  muriatic,  from  muria,  the  Latin  name  of  sea  salt.  It 
is  also  called  the  marine  acid,  and  the  spirit  of  sea  salt(28).  Although  the 
muriatic  acid  had  been  long  known,  it  was  first  obtained  in  a  state  of  purity 
by  Dr  Priestley,  who  discovered  that  it  was  a  permanent  gas.  In  this  form 
it  is  extremely  suffocating  and  corrosive,  very  rapidly  destroying  the  life  of 
an  animal  confined  in  it.  The  liquid  acid,  some  of  which  I  have  in  this  bottle, 
consists  of  muriatic  acid  gas,  absorbed  and  condensed  by  water,  one  pint  of 
•which  will  take  up  between  four  and  five  hundred  pints  of  the  gas(29). 


23.  What  remarkable  properties  does  the Jluo-siUcic  acid  possess? 

24.  What  is  said  respecting  the  composition  of  fluoric  acid? 

25.  Why  are  we  justified  in  concluding  that  it  is  a  compound? 

26.  In  what  combination  is  muriatic  acid  found  most  abundantly? 
£7.  Who  was  its  discoverer,  and  by  what  means  did  he  obtain  it? 

28.  What  is  said  respecting  the  names  given  to  it? 

29.  What  is  the  form,  and  what  the  properties  of  the  pure  acid? 


236 


CONVERSATIONS  ON  CHEMISTRY. 


Caroline.  Then  we  cannot  collect  this  gas  by  means  of  the  pneumatic 
cistern,  as  the  water  would  absorb  it  as  fast  as  it  was  produced. 

Mrs  B.     A  mercurial  trough,   or  cistern,    is 

used    for    that   purpose;    but    as    the    specific   Collecting  gaseous  Muri- 
gravity    of   the    gas    exceeds    that   of    atmos-  atic  Acid. 

pheric  air,  it  can  be  collected  in  a  bottle,  as  we 
formerly  collected  carbonic  acid  (p.  157)(30); 
it  is  necessary,  however,  carefully  to  avoid  the 
fumes.  I  have  now  filled  this  bottle,  and  will 
invert  it,  placing  the  mouth  of  it  in  water. 

Emily.  How  rapidly  the  water  ascends  and 
fills  the  bottle.  I  expected  to  see  the  gas  ab- 
sorbed, but  not  so  suddenly.  I  observe  that 
whenever  this  gas  comes  in  contact  with  the  at- 
mosphere, a  white  cloud  is  formed,  although  the 
gas  itself  is  colourless  and  invisible.  This,  I 
suppose,  arises  from  its  combining  with  the  A 
watery  vapour  which  it  finds  in  the  air.  [A.  Flask  containing  mu- 

Mrs  JB.     Certainly;  and  from  the  extreme  ea-       riate  of  soda  and  sulphu- 
gerness   with  which  this  gas  unites  with  water,      ric  acid.] 
so  much  heat  will  be  set  free,  as  to  melt  a  por- 
tion of  ice  or  snow,  placed  in  it,  as  rapidly  as  though  it  were  thrown  into  a 
fire(31). 

An  apparatus,  called  Woulfe's  apparatus,  i s  advantageously  used  in  pre- 
paring the  liquid  acid.  It  is  employed,  in  fact,  in  all  those  processes  where 
liquids  are  to  be  impregnated  by  gases,  and  you  ought  therefore  to  un- 
derstand its  operation.  This  apparatus  is  made  in  various  forms,  but  that 
which  I  have  on  the  table  is  the  most  common.  The  bottles,  you  perceive, 
are  furnished  with  three  necks,  and  they  contain  a  portion  of  water,  which 
is  to  be  impregnated  with  the  gas. 

Woulfe's  Apparatus. 


When  muriatic  acid  is  to  be  formed,  common  salt  is  put  into  the  re- 
tort [A],  and  sulphuric  acid,  a  little  diluted,  poured  upon  it.  On  apply- 
ing heat  to  the  retort,  the  gaseous  muriatic  acid  passes  into  the  globe  [B]< 
and  in  that  is  deposited  any  condensible  vapour  which  would  render  the 
acid  impure.  From  this  globe  the  gas  passes  through  the  bent  tube  [C], 
which  should  terminate  above  the  surface  of  the  water  in  the  first  bottle[D]. 
This  water  absorbs  a  portion  of  the  gas,  and  the  remainder  passes  through 
the  tube  [E],  which  dips  below  the  water  in  the  next  bottle  [F].  In  this  way 
any  number  of  bottles  may  be  connected  together,  and  the  process  con- 
tinued until  the  water  in  each  is  completely  saturated.  To  promote  the 


30.  By  what  methods  may  this  gaseous  acid  be  collected? 

31.  \Vhatoccurswhenitcomesincontactwithwater  with  air,  or  with  ice  > 


ON  CHLORINE.  237 

absorption  of  the  gas,  the  bottles  may  be  surrounded  with  ice.  Any- 
atmospheric  air,  or  other  gas,  which  the  water  will  not  absorb,  may  be 
allowed  to  escape  at  the  tube  [G]  in  the  last  bottle. 

Caroline.  You  have  explained  the  use  of  the  bent  tubes,  but  not  of  the 
straight  ones  which  pass  up  from  the  middle  neck. 

J\frs  JB.  These  tubes,  called  safety  tubes,  are  intended  to  admit  atmos- 
pheric air  into  the  bottles,  when  its  admission  may  become  necessary.  As, 
for  instance,  when,  from  diminished  action  in  the  retort,  the  gas  ceases  to 
come  over.  A  vacuum  may  then  be  produced  in  the  globe  [B],  as  the  wa- 
ter in  the  first  bottle  [D]  will  be  likely  to  absorb  the  portion  of  gas  which 
it  contained.  The  pressure  of  the  atmosphere,  acting  through  the  tubes 
[G,E  and  C]  would  then  cause  the  fluid  in  the  first  bottle  to  pass  over  into  the 
globe,  and  it  would  be  spoiled  by  mixing  with  the  impurities  which  the  globe 
had  detained.  The  central  tubes  prevent  this  from  taking  place;  for,  the 
air  of  the  atmosphere  will  rush  in  through  them,  and  bubble  up  through 
the  fluid  into  which  they  dip,  whenever  a  vacuum  is  formed  in  either  of 
the  bottles(32). 

In  using  this  apparatus  all  the  tubes  must  be  made  to  fit  air  tight.  In 
the  manufactories  where  muriatic  acid  is  made  upon  a  large  scale,  vessels 
of  iron,  and  of  earthenware,  are  used,  instead  of  those  of  glass.  A  little  iron 
is  usually  contained  in  the  acid  of  commerce,  and  from  this  cause  it  assumes 
a  yellow  colour(33). 

Caroline.  As  this  acid  contains  a  substance  with  which  we  are  at  pre- 
sent unacquainted,  I  feel  a  good  deal  of  interest  upon  the  subject  of  its  de- 
composition. 

Mrs  J3.  And  to  gratify  you  in  this  particular,  I  will  omit  all  further 
notice  of  the  muriates,  until  you  have  obtained  some  information  respect- 
ing chlorine. 

CHLOHIKE  was  discovered  by  the  eminent  Swedish  chemist  SCHEELE,  and 
the  process  by  which  he  obtained  it  is  still  pursued.  Strong  muriatic  acid 
is  mixed,  in  a  retort,  with  about  half  its  weight  of  theperoocide  (black  oxide) 
of  manganese:  chlorine  gas  will  immediately  begin  to  escape,  and  may  be 
collected  over  the  pneumatic  cistern,  provided  the  water  in  it  be  heated 
to  eighty  or  ninety  degrees  of  Fahrenheit's  scale.  This  is  necessary, 
as  water  at  a  lower  temperature  absorbs  a  portion  of  the  gas,  and  if 
quite  cold,  will  take  up  its  own  volume;  which  it  will  give  out  again  when 
heated.  As  chlorine  is  much  heavier  than  atmospheric  air,  it  may,  like 
muriatic  acid  gas,  be  collected  in  bottles  standing  upright,  which,  when  fill- 
ed, should  be  closed  by  well  ground  stoppers.  The  fumes  that  arise 
from  chlorine  should  be  carefully  avoided,  as  they  are  not  merely  unplea- 
sant, but  deleterious(34). 

Emily.  So  far  it  appears  to  resemble  the  muriatic  acid  itself,  from  which 
it  is  obtained. 

.Mrs  _B.  You  will  find  however  that  it  is  a  very  different  substance,  and 
that  in  its  chemical  relationships  it  bears  a  strong  affinity  to  oxygen;  being, 
like  it,  a  supporter  of  combustion,  converting  some  combustibles  into  chlo- 
rides, a  class  of  compounds  which  are  analogous  to  oxides,  and  combining 
with  others  of  them  in  such  proportions  as  to  produce  acids(35). 

We  have  now  a  sufficient  quantity  of  chlorine  collected  to  show  its 
properties,  some  of  which  are  very  peculiar. 

Caroline.      It  already  exhibits  one  peculiarity,  as,  unlike  all  the  other 


32.  Describe  the  construction  and  the  use  of  Woulfe's  apparatus. 

33.  From  what  cause  does  the  muriatic  acid  of  commerce  appear  yellow? 

34.  Who  was  the  discoverer  of  chlorine,  and  by  what  method  and  under 
what  precautions  may  it  be  obtained? 

35.  What  is  said  respecting  its  analogy  with  oxygen? 


238  CONVERSATIONS  ON  CHEMISTRY. 

gases  which  you  have  prepared,  it  is  coloured,  the  bottles  which  contain 
it  assuming  a  greenish-yellow  appearance. 

Mrs  B.  It  was  this  character  that  suggested  to  Davy  the  name  by 
•which  it  is  now  called;  the  term  chlorine  being  derived  from  a  Greek 
word  signifying  green.  It  had  been  previously  called  oxygenized  or  oxy- 
muriatic  add,  the  reason  of  which  will  hereafter  appear(36). 

I  have  said  that  this  gas  is  a  supporter  of  combustion,  and  in  fact,  with 
the  exception  of  carbon,  all  combustibles  burn  in  it.  Many  of  them  will  take 
fire  spontaneously,  when  placed  in  a  vessel  containing  it,  without  requir- 
ing to  have  their  temperatures  previously  elevated(37). 

Emily.  Are  not  the  thin  metallic  leaves  which  you  are  taking  up  called 
Dutch  metal,  or  Dutch  gold  leaf  ? 

Mrs  B.  They  are.  And  I  will  now  immerse  one  of  them  in  a  jar  of 
the  chlorine,  and  you  see  that  it  immediately  takes  fire. 

Emily.  Yes,  indeed  it  did,  and  the  combustion  too  was  very  rapid.  I 
suppose  a  chloride  has  been  formed;  but  a  chloride  of  what? 

Mrs  B.  This  Dutch  metal  consists  principally  of  copper,  and  of  course 
its  chloride  is  the  main  product.  Other  metals  in  thin  leaves  burn  in  the 
same  way.  In  their  combustion  they  also  are  converted  into  chlorides.  I 
will  next  drop  some  antimony,  and  then  some  zinc,  in  fine  filings,  into  separate 
portions  of  the  gas,  and  each  of  them  will  inflame  and  burn  with  great 
brilliancy(38). 

Caroline.  They  form  a  complete  shower  of  fire,  and  were  it  not  for  the 
excessively  disagreeable  smell  of  the  gas,  the  experiment  would  be  altogether 
a  most  pleasing  one. 

Mrs  B.  We  will  try  the  same  experiment  with  the  piece  of  phosphorus 
•which  I  have  in  this  copper  ladle.  You  had  better  stand  on  this  side,  that 
when  I  open  th»  jar  the  wind  may  blow  the  vapour  from  you.  . 

Emily.  It  takes  fire  and  burns  beautifully,  although  by  no  means  so 
splendidly  as  in  oxygen  gas(39). 

Mrs  B.  These  examples  of  combustion  must  suffice;  as  I  wish  now  to 
show  you  the  extraordinary  power  of  chlorine  in  destroying  colour;  or  in  other 
words,  its  bleaching  property.  In  one  of  these  jars  of  the  gas  I  will  place  a 
red  rose,  and  in  the  other  a  piece  of  printed  calico,  and  its  influence  will  be 
very  quickly  seen. 

Emily*  The  rose  is  already  nearly  white,  and  the  calico  is  becoming  so 
on  its  edges(40). 

Mrs  B.  There  are  but  few  colours  which  resist  this  agent.  And  all 
those  which  are  derived  from  animal  or  vegetable  substances  are  completely 
discharged  by  it.  This  property  of  chlorine  has  been  turned  to  good  account 
in  the  manufacture  of  cotton  and  linen  goods,  of  paper,  and  of  many  other 
articles  which  require  to  be  bleached(41). 

Caroline.  I  do  not  understand  in  what  way  the  black  oxide  of  manganese 
operates,  in  the  conversion  of  muriatic  acid  into  chlorine.  This  oxide,  I 
know,  has  a  tendency  to  part  with  oxygen,  but  I  do  not  perceive  how  this 
can  produce  the  decomposition  in  question. 

Mrs  B.     You  recollect  the  composition  of  muriatic  acidr 

Caroline.  Certainly.  You  informed  us  that  it  consists  of  hydrogen  and 
chlorine. 

Mrs  B.     You  will  readily  understand  in  what  way  the  decomposition  is 


36.  Why  is  it  named  chlorine,  and  what  was  it  formerly  called? 

37.  What  is  remarked  respecting  its  power  of  supporting  combustion? 

38.  What  experiments  are  detailed,  and  what  is  their  result? 

39.  How  will  phosphorus  be  affected  if  placed  in  this  gas? 

40.  What  evidence  is  given  of  the  bleaching  power  of  chlorine? 

41.  To  what  use  has  it  been  applied  in  consequence  of  this  property? 


ON  CHLORINE.  239 

effected.  The  peroxide  of  manganese  parts  with  a  portion  of  its  oxygen, 
which  combines  with  the  hydrogen  of  the  muriatic  acid,  forming  water* 
The  acid  is  of  course  decomposed,  and  the  chlorine  set  at  liberty(42). 

Such  is  the  theory  of  its  action;  and  without  waiting  to  puzzle  you  with  num- 
bers, I  will  werely  observe  that  when  examined  by  the  law  of  definite  pro- 
portions, it  is  in  perfect  accordance  therewith.  After  the  decomposition  of 
the  acid,  and  the  disengagement  of  its  chlorine,  there  remains  in  the  retort 
a  muriate  of  manganese;  that  salt  being  formed  by  the  combination  of  a 
portion  of  the  muriatic  acid  with  the  protoxide  of  manganese.  The  attrac- 
tion of  chlorine  for  hydrogen,  and  of  muriatic  acid  for  the  protoxide  of 
manganese  is  the  cause  of  the  decomposition(43). 

Caroline.  I  am  still  thinking  of  the  old  name  of  chlorine,  oxymuriatio 
acid.  This  name  seems  to  point  out  a  combination  between  muriatic  acid 
and  oxygen,  which,  if  it  took  place,  would  account  for  the  fact  that  many  of 
the  properties  of  oxygen  are  possessed  by  chlorine. 

Jlfrs  B.     At  the  period  of  the  adoption  of  this  name,  muriatic  acid  was 
believed  to  be  an    undecompounded    substance,    but   capable    of  forming 
a   combination  with  oxygen;   and   it  was  imagined  that  in  the  process  by 
j  which  chlorine   is  procured,  oxygen  was   supplied  to   it  by  the  oxide  of 
manganese,  and  that  whenever  it  parted  with  this  oxygen  it  returned  to  the 
j  state  of  muriatic  acid(44).     A  number  of  facts  seemed  to  justify  this  opinion; 
j  I  will  mention  one  only.     When  chlorine  (oxymuriatic  acid)  had  been  em- 
j  ployed   in  bleaching,  it  was  found  that  it  eventually  ceased  to  produce  this 
j  effect,  in  consequence  of  its  passing  into  the  state  of  muriatic  acid.     As 
:  oxygen  was  known  to  be  the  agent  upon  whose  influence  the  discharge  of 
colours  principally  depends,   it   was  a  very  natural   conclusion,   that   the 
bleaching  power  of  chlorine  (oxymuriatic  acid)  resulted  from  the  facility 
with  which  it  was  supposed  to  furnish  oxygen  in  a  nascent  state,  which,  com- 
bining with  the  colouring  matter,  effected  its  removal(45). 

Caroline.  1  am  somewhat  afraid  of  my  own  confidence;  but  it  seems  to 
me  that  the  fact  which  you  have  stated,  lends  no  feeble  support  to  the  old 
theory.  How  can  chlorine  give  out  oxygen,  if  it  does  not  contain  any? 

•Mrs  B.  If  it  takes  hydrogen  from  water,  oxygen  is  given  out  by  its 
agency,  although  not  from  its  own  substance.  Now  in  all  those  processes 
in  which  chlorine  assumes  the  form  of  muriatic  acid,  water  is  present;  and  if 
by  seizing  upon  its  hydrogen  the  chlorine  returns  to  the  state  of  muriatic 
acid,  the  nascent  oxygen  of  the  water  will  produce  all  the  effects  which  were 
formerly  ascribed  to  it  when  it  was  supposed  to  be  derived  from  the  decom- 
position of  oxymuriatic  acid.  Perfectly  dry  chlorine  does  not  produce  any 
change  in  coloured  substances,  but  as  soon  as  moisture  is  admitted,  the  bleach* 
ing  operation  commences(46). 

Caroline.  It  seems  very  curious,  however,  that  all  the  effects  of  chlorine 
should  be  so  readily  accounted  for  upon  either  theory;  and  I  should  think 
that  it  is  a  subject  still  worthy  of  examination. 

Mrs  B.  There  are  some  few  facts  which,  when  placed  before  you,  may 
not  appear  to  be  so  reconcilable  with  the  idea  of  the  compound  nature 
of  chlorine  as  that  already  stated.  Three  of  these  I  will  mention,  and  then 
dismiss  the  controverted  point  altogether;  proceeding  in  all  our  subsequent 
explanations  on  the  received  opinion  that  chlorine  is  an  elementary  body. 


42.  How  does  the  oxide  of  manganese  aid  in  decomposing  muriatic  acid? 

43.  What  remains  in  the  retort  after  the  chlorine  has  escaped? 

44.  Chlorine  was  formerly  called  oxymuriatic  acid,  what  was  the  reason 
for  applying  this  name  to  it? 

45.  What  fact  was  calculated  to  sustain  this  opinion? 

46.  How  are  the  disengagement  of  oxygen  and  the  production  of  muriatio 
aeid  now  accounted  for? 


240  CONVERSATIONS  ON  CHEMISTRY. 

Caroline.  I  shall  be  obliged  to  you  for  these  facts^and  will  promise  you 
not  to  urge  any  more  of  my  crude  objections;  but  to  be  what  I  ought  to  be, 
a  listener  and  a  learner. 

JWrs  B.  When  equal  measures  of  chlorine  and  of  hydrogen  gases  (both 
perfectly  freed  from  moisture)  are  mixed  together,  if  an  electric  spark  be 
passed  through  the  mixture  they  instantaneously  combine,  heat  and  light  are 
emitted,  and  muriatic  acid  is  formed.  The  weight  of  the  acid  will  be  exactly 
equal  to  that  of  the  two  gases,  and  no  oxygen  will  be  obtained.  Any  other 
mode  of  igniting  the  gases  will  answer  equally  well(47). 

If  charcoal   in  a  state  of  intense  ignition  be  kept  in   chlorine,  the  gas 
suffers  no  change  whatever.      The  charcoal   does  not  acquire  any  oxygen, 
and  as  it  will  not  burn  in  chlorine,  no  chemical  effect  whatever  is  pro-  * 
duced. 

Emily.  That  appears  very  remarkable,  as  ignited  charcoal  decomposes 
almost  every  oxide.  If  chlorine  contained  oxygen  loosely  combined,  it  cer- 
tainly would  give  it  up  to  the  charcoal(48). 

Mrs  B.  Again;  if  chlorine,  perfectly  dry,  be  exposed  in  a  glass  re- 
ceiver to  the  action  of  light,  no  change  whatever  will  be  produced  in  it. 
But  if  any  moisture  be  present,  muriatic  acid  will  be  generated,  and 
oxygen  gas  set  at  liberty.  In  the  sunshine  this  change  is  effected  very 
quickly;  more  slowly  in  a  feeble  light,  and  in  the  dark  not  at  all.  It  is 
necessary,  therefore,  after  we  have  obtained  chlorine  over  water,  to  exclude 
the  vessels  containing  it  from  the  action  of  light,  or  it  will  soon  be  changed 
in  its  properties(49). 

Caroline.  These  facts  seem  indeed  to  give  a  strong  support  to  the  ele- 
mentary character  of  chlorine.  The  action  of  light  in  effecting  the  compo- 
sition of  muriatic  acid  is  a  circumstance  which  appears  full  of  interest. 

JUrs  B.    You  have  seen  many  instances  of  the  chemical  agency  of  light,  v 
and  certainly  its  action  on  chlorine  is  not  one  of  the  least  striking.     The  * 
mixture  of  dry  chlorine  and  hydrogen,  which  will  ignite  by  the  electric 
spark,  will  explode  also  the  moment  the  direct  solar  ray  is  allowed  to  fall 
upon    a  glass   vessel    containing  them,   although   in  the   diffused   light  of 
day  their  union   is  effected  but  slowly(SO). 

Emily.     Does  there  appear  to  be  any  other  compound  of  chlorine  and  'k 
hydrogen,  excepting  the  muriatic  acid? 

J\frs  B.  No;  and  in  this  the  combination  is  believed  to  consist  of  a  single 
atom  of  each  element.  And  as  in  muriatic  acid  the  weight  of  the  chlorine  is 
thirty-six  times  that  of  the  hydrogen,  the  equivalent  number,  or  atomic 
weight,  of  chlorine  will  be  thirty-six;  and  when  to  this  we  add  one,  the 
weight  of  an  atom  of  hydrogen,  we  have  thirty-seven  as  the  equivalent  o 
muriatic  acid(51). 

Before  closing  this  conversation  I  will  mention  the  process  by  which 
chlorine  is  obtained  in  the  manufactories  for  the  purpose  of  bleaching,  as  ii 
differs  from  that  by  which  we  have  procured  it. 

Three  parts  of  common  salt  are  mixed  with  one  part  of  the  peroxidt 
of  manganese  in  powder.      This  mixture  is  put  into  a  retort,  and  two  parts 
of  sulphuric  acid,  diluted  with  an  equal  weight  of  water,  are  poured  upon  it. 
The  sulphuric  acid  disengages   the  muriatic  acid  from  the  muriate  of  soda 
the  oxygen  cf  the  manganese  combines  with  the  hydrogen  of  a  part  of  the 


47.  How  may  muriatic  acid  be  formed  by  the  direct  union  of  chlorine  am 
hydrtfgen? 

48.  What  is  observed  respecting  charcoal  ignited  in  chlorine? 

49.  What  is  remarked  of  the  action  of  light  upon  chlorine? 

50.  What  effect  will  it  produce  on  a  mixture  of  chlorine  and  hydrogen? 

51.  What  are  the  atomic  weights  of  chlorine  and  of  muriatic  acid? 


ON  THE  COMPOUNDS  OF  CHLORINE.  241 

muriatic  acid,  and  reduces  it  to  the  state  of  chlorine,  which  passes  off  in  tb.e 
gaseous  form.     Can  you  tell  me  what  will  then  remain  in  the  retort(52)  ? 

Caroline.  I  think  I  can;  for  although  two  operations  are  simultaneously 
performed,  you  have  to-day  explained  themhoth  to  us.  The  sulphuric  acid 
unites  with  the  soda  of  the  common  salt,  and  forms  a  sulphate  of  soda,  and 
whilst  a  part  of  the  muriatic  acid  which  is  expelled  from  the  soda  is  decompos- 
ed, in  parting  with  its  hydrogen  to  the  oxygen  of  the  manganese,  another  part 
combines  with  the  protoxide  of  manganese,  forming  with  it  a  muriate  of  that 
metal.  The  sulphate  of  soda  and  the  muriate  of  manganese,  in  a  state  of 
mixture,  must  therefore  he  found  in  the  retort(53). 

Mrs  B.  1  was  apprehensive  that  the  subject  of  our  present  conversa- 
tion would  have  presented  greater  difficulties  than  you  appear  to  have  ex- 
perienced in  understanding  it.  By  the  combination  of  industry  and  method, 
you  already  have  done  much  towards  attaining  a  knowledge  of  some 
chemical  changes  which  are  among  the  most  intricate  that  this  science 
presents.  Still,  at  our  next  meeting,  you  will  find  that  the  subject  is  not  yet 
exhausted. 


CONVERSATION   XXIV. 

ON     THE    COMPOUNDS     OF     CHLORINE,    AND     ON    IODINE, 
BROMINE,  AND  THEIR  COMPOUNDS. 

Chlorides  and  Muriates.  Hydrochloric  Acid.  Chlorine  and  Oxygen. 
Protoxide  of  Chlorine.  Chloric  and  Perchloric  Jlcids.  Chloride  of  Nitro- 
gen. Hydrocarburet  of  Chlorine.  Chlorate,  or  Hyperoxymuriate  of  Potassa. 
A fords  pure  Oxygen.  Match-lights.  Combustion  of  Phosphorus  under 
Water.  Detonations  -with  Sulphur,  Phosphorus,  and  Metals.  Percussion 
Po-wder.  Muriate  of  Soda,  or  Chloride  of  Sodium.  Sea  Water.  Sources 
and  Uses  of  Common  Salt.  Muriate  of  Ammonia.  Muriate  of  Lime. 
Chloride  of  Lime.  Its  Bleaching  and  Disinfecting  Properties.  Aqua  Regia, 
or  Nitro-muriatic  Acid.  Dissolution  of  Gold.  Corrosive  Sublimate,  and 
Calomel.  Iodine  and  Bromine.  Their  Properties  and  Combinations. 
Are  Electro-negative  Bodies.  Uses  of  Iodine. 

Caroline.  It  seems  to  me,  Mrs  B.  that  in  operating  with  chlorine,  it  must 
sometimes  be  difficult  to  foretell  whether  you  are  about  to  form  a  chloride 
or  a  muriate.  For  as  water  is  contained  in  the  atmosphere,  and  in  the  gases 
generally,  the  chlorine  may  combine  with  the  hydrogen  of  this  water,  and 
form  muriatic  acid,  without  our  being  aware  of  the  change. 

Mrs  B.  The  difficulty  which  you  have  anticipated  does  actually  exist. 
And  there  are  cases  in  which  chemists  have  not  been  able  to  determine, 
absolutely,  to  which  of  the  two  classes  certain  bodies  belong.  For  a 
substance  which  is  actually  a  chloride  whilst  it  remains  solid,  may,  when 
dissolved  in  water,  obtain  hydrogen,  and  thus  become  a  muriate.  I  wish 
you  to  take  special  notice  of  this  fact,  and  I  shall  shortly  direct  your  attention 
to  it  more  particularly  in  my  remarks  upon  common  salt(i). 

Emily.  There  seems,  in  this  case,  to  be  some  discrepancy  in  the  names 
which  you  employ.  That  of  muriatic  acid  ^certainly  gives  no  indication 
of  the  elements  of  which  this  acid  is  compounded. 


52.  How  is  chlorine  usually  obtained  for  bleaching? 

53.  What  will  remain  in  the  retort  after  this  process? 

1.  What  difficulty  may  exist  in  tracing  the  operations  of  chlorine  f 


242  CONVERSATIONS  ON  CHEMISTRY. 

Mrs  B.  When  the  new  nomenclature  was  adopted,  the  composition  of 
this  acid  was  unknown,  and  remained  so  for  many  years.  The  name  muriatic 
acid  had  during  this  time  become  so  familiar  as  to  render  a  change  both 
difficult  and  inconvenient.  The  French  chemists  call  it  hydrochloric  acid, 
and  its  salts  hydrochlorates;  but  as  we  continue  to  use  the  old  name,  you  have 
only  to  charge  your  memory  with  the  recollection  of  the  composition  of  the 
acid,  and  all  erroneous  conclusions  will  be  avoided(2). 

I  have  told  you  that  it  is  not  with  hydrogen  alone  that  chlorine  forms  an 
acid,  its  union  with  oxygen  producing  a  similar  result.  There  are  in  fact  four 
known  compounds  of  oxygen  and  chlorine.  These  substances  are  all 
characterized  by  the  feeble  attraction  of  their  constituents,  very  slight  causes 
effecting  their  decomposition.  Their  names  and  composition  are  shown  in 
this  table(3). 


Compounds  of  Chlorine  and  Oxygen.. 

1.  Protoxide  of  chlorine  (euchkrine) 
9,.  Peroxide  of  chlorine, 

3.  Chloric  acid, 

4.  Perchloric  acid, 


Chlorine. 

36,  1  at. 
36,  1  at. 
36,  lat. 
36,  1  at. 


Oxygen. 

8,  1  atom 
32,  4  atoms 
40,  5  atom- 
56,  7  atoms 


Atomic  -weight 
of  compound. 

44 

68 

76 

92(4). 


Caroline.  The  large  number  of  atoms  of  oxygen  in  some  of  these  com- 
pounds, and  the  facility  with  which  it  is  separated,  must,  I  apprehend,  cause 
them  sometimes  to  act  with  great  power,  particularly  upon  combustibles. 

Mrs  JS.  You  will  find  your  conjecture  fully  verified;  but  as  substances 
so  easily  decomposed  cannot  exist  in  nature,  they  are  all  under  the  control 
of  the  chemist,  being  his  own  artificial  productions(S).  The  PROTOXIDE 
OF  CHLORINE,  sometimes  called  euchlorine,  is  a  gas,  the  colour  of  which 
is  similar  to  that  of  chlorine,  but  of  a  much  deeper  shade.  It  is  extremely 
explosive;  the  warmth  of  the  hand,  or  its  agitation  in  pouring  it  from  one 
vessel  into  another  being  sufficient  to  make  it  explode.  The  PEROXIDE 
OF  CHLORIXE  is  also  a  gas,  but  of  a  still  more  intense  colour(6). 

Its  explosion  is  more  powerful  than  that  of  the  protoxide,  but  it  does  not 
take  place  below  the  heat  of  boiling  water.  Both  these  gases  possess  pow- 
erfully bleaching  properties,  and  in  either  of  them  phosphorus  will  sponta- 
neously burst  into  flame(7). 

Emily.  These  compounds  appear  to  be  dangerous  affairs  to  meddle 
with,  and  ought  not  to  be  tou  ned  by  inexperienced  hands. 

Mrs  B.  There  are  other  combinations  of  chlorine  which  are  still  more 
•violent  than  these.  Fortunately,  however,  we  may  safely  talk  about  such 
compounds,  although  the  handling  of  them  might  be  attended  with  some 
vi  sk. 

CHLORIC  ACID  is  generally  formed  by  passing  chlorine  through  solutions 
of  the  alkalies  and  alkaline  earths.  It  is  in  its  combinations  with  these 
bases,  called  chlorates,  that  we  shall  witness  its  most  important  proper- 
ties^). When  obtained  in  a  separate  form  it  is  a  colourless  fluid,  possess- 
ing all  the  characteristic  properties  of  the  acids.  It  is  so  easily  decomposed, 
that  it  has  been  but  little  examined.  Perchloric  acid  is  still  less  known, 
although  the  existence  of  such  a  compound  is  considered  as  established(9). 


2.  What  is  observed  respecting  the  names  of  muriatic  acid? 

3.  How  many  combinations  of  chlorine  and  oxygen  are  known? 

4.  What  are  they  named,  and  how  are  they  constituted? 

5.  What  is  observed  respecting  the  facility  of  their  decomposition? 

6.  What  properties  characterize  the  protoxide  of  -chlorine? 

7.  What  particulars  are  mentioned  respecting  \heperoxide? 

8.  By  what  process  is  chloric  acid  usually  produced? 

9.  What  further  is  remarked  respecting  chloric  and  perchloric  acids? 


ON  CHLORATE  OF  POTASSA.  243 

Caroline.  Notwithstanding  chlorine,  in  its  simple  form,  is  not  presented 
to  us  by  nature,  yet  if  in  her  operations  its  compounds  are  as  active  as  those 
prepared  by  the  chemist,  it  may  certainly  claim  a  place  in  company  with  that 
all  pervading  principle,  oxygen. 

Mrs  B.  The  chemical  history  of  chlorine  is  one  of  great  interest,  but  at 
the  same  time  of  great  intricacy;  and  the  consideration  of  it  has  there- 
fore been  deferred  until  most  of  the  other  agents  had  been  made  known  to 
you.  The  changes  which  it  undergoes,  or  produces,  are  so  involved,  as 
not  to  admit  of  a  systematic  classification,  and  of  course,  I  shall  not  at- 
tempt any. 

I  shall  next  notice  some  of  the  chlorides,  and  may  probably  find  it  con- 
venient to  incorporate  both  the  chlorates  and  muriates  with  them. 

CHLORIDE  OF  NITIIOGEX  is  an  oil-like  fluid,  produced  by  the  union  of  the 
bases  of  the  two  gases.  When  the  mouth  of  a  receiver  containing  chlorine,  is 
placed  over  a  solution  of  muriate  of  ammonia,  the  alkali  is  gradually  decom- 
posed, its  hydrogen  unites  with  a  portion  of  the  chlorine  and  forms  muriatic 
acid,  whilst  its  nitrogen  combines  with  another  portion  of  chlorine,  pro- 
ducing the  chloride  ofnitrogen(lQ).  This  liquid  first  forms  a  film  upon  the 
surface  of  the  solution,  and  afterwards  sinks  through  it  in  drops.  A  single 
drop,  the  size  of  a  pea,  if  incautiously  handled  produces  a  dangerous  ex- 
plosion. The  same  effect  is  likewise  caused  by  mere  contact  with  olive  oil, 
and  with  many  other  combustibles,  although  it  is  not  induced  by  heat  alone, 
until  the  temperature  exceeds  200°.  The  chloride  of  nitrogen  is  converted, 
by  explosion,  into  a  mixture  of  nitrogen  gas  and  chlorine.  Its  discoverer 
Dulong,  and  Sir  H.  Davy,  were  both  seriously  injured  by  experimenting 
with  this  most  violent  of  all  the  explosive  compounds(ll). 

Emily.  I  recollect  another  compound  resembling  oil,  which  you  told  us 
(p.  162)  was  produced  by  the  combination  of  olefiant  gas,  or  heavy  carbu- 
retted hydrogen,  with  chlorine.  This,  like  the  combination  of  nitrogen  and 
chlorine,  is,  I  suppose,  denominated  a  chloride. 

Mrs  B.  This  oily  substance  is  not  called  a  chloride,  but  is  frequently 
designated  by  the  term  hydrocarburet  of  chlorine.  To  form  it,  equal  mea- 
sures of  chlorine  and  of  olefiant  gas  are  mixed  together;  whereupon  the 
two  gases  gradually  disappear,  and  there  is  generated  a  yellow  liquid  like 
oil.  This  substance,  however,  does  not  possess  any  of  the  properties  of  the 
chloride  of  nitrogen,  nor  is  it  properly  an  oil(12). 

Carbon,  sulphur,  phosphorus,  and  some  other  articles  may  also  be  con- 
verted into  chlorides,  but  I  shall  pass  them  by,  and  proceed  to  a  very  in- 
teresting salt,  formerly  called  the  hyperoxymuriate  ofpotassa,  but  now  de- 
nominated  chlorate  of  potassa. 

CHLORATE  OF  POTASSA,  better  known  as  the  hyperoxymuriate  of  potassa,  may 
be  conveniently  formed  in  Woulfe's  apparatus  (p.  236).  By  putting  into  the 
bottles  a  solution  of  caustic  potash,  and  passing  into  it  a  stream  of  chlorine 
gas,  until  the  solution  is  saturated,  the  salt  in  question  will  be  produced(13). 

Caroline.  But  how  can  this  process  form  a  chlorate?  I  should  suppose 
that,  to  effect  this,  you  must  pass  chloric  acid  into  the  solution  of  potash. 

Mrs  B.  Recollect  that  water  is  present,  and  you  may  find  that  by  in- 
voking its  aid  your  difficulty  will  be  removed.  The  hydrogen  of  the  water 
unites  with  a  part  of  the  chlorine,  and  forms  muriatic  acid,  which  acid  com- 
bining with  potash  becomes  muriate  of  potash.  The  oxygen  liberated  from 
the  decomposed  water,  and  presented,  in  its  nascent  state,  to  the  chlorine, 


10.  By  what  process  may  we  form  the  chloride  of  nitrogen  ? 

11.  What  is  its  appearance,  and  what  are  its  properties? 

12.  What  is  said  of  the  oil-like  substance  from  olefiant  gas? 

1 3.  By  what  process  may  hyperoxymuriate,  or  chlorate,  of  potassa  be 
formed? 


244  CONVERSATIONS  ON  CHEMISTRY. 

combines  with  it;  and  this  uniting  with  a  part  of  the  potash,  produces  chlo- 
rate of  potassa(!4). 

Caroline.  But  I  perceive  what  appears  to  me  a  strong  objection  to  that 
explanation.  Chloric  acid  contains  one  atom  of  chlorine  united  to  five  atoms 
of  oxygen,  and  yet  each  atom  of  the  decomposed  water  parts  with  but  one 
atom  of  oxygen.  Whence,  then,  can  the  chloric  acid  derive  the  five  atoms 
required  to  produce  it(15)? 

Emily.  Were  muriatic  acid  alone  generated,  oxygen  alone  would  be 
given  out.  Perhaps,  therefore,  there  may  be  a  large  portion  of  muriatic,  and 
but  a  small  portion  of  chloric  acid  formed;  and  this,  you  know,  might  af- 
ford a  sufficient  quantity  of  oxygen  to  give  the  five  atoms  necessary  to  its 
composition. 

Mrs  B.  And  such  appears  to  be  the  fact.  The  quantity  of  muriate  of 
potassa,  which  we  obtain,  is  five  times  as  great  as  that  of  the  chlorate,  and 
consequently,  there  will  be  oxygen  enough  liberated  to  produce  this  pro- 
portionate quantity  of  chloric  acid(16). 

The  chlorate  of  potassa  is  much  less  soluble  than  the  muriate,  the  conse- 
quence of  which  is,  that,  during  the  process,  a  large  portion  of  the  chlorate  is 
precipitated  in  beautiful  pearly  scales,  such  as  you  see  in  this  phial. 
These  crystals  are  washed  to  free  them  from  any  adhering  muriate  of  po- 
tassa, and  may,  when  dried  in  a  gentle  heat,  be  considered  as  the  pure  chlo- 
rate of  potassa(17).  Between  this  salt  and  nitre,  there  is  a  strong  resem- 
blance; as  there  is,  indeed,  between  the  nitrates  and  the  chlorates  generally. 

Emily.  This  may  well  be  supposed,  as  they  both  contain  a  large  quan- 
tity of  oxygen  in  a  state  of  very  loose  combination. 

Jlfrs  B.  And  in  the  chlorates  the  union  is  more  loose  than  in  the  nitrates; 
in  consequence  of  which  many  inflammables  will  decompose  the  formex, 
which,  under  similar  circumstances,  would  not  affect  the  latter,  as  you 
will  presently  see(18). 

Caroline.  Can  we  not  decompose  the  chlorate  and  obtain  its  acid,  by 
pouring  upon  it  sulphuric  acid,  just  as  nitric  acid  was  obtained  from  nitre  ? 

Mrs  B.  The  decomposition  in  this  case  does  not  stop  at  the  production 
of  the  acid.  The  chloric  acid  is  not  merely  separated  from  the  potash,  but 
is  itself  decomposed,  and  explodes,  shivering  to  atoms  any  glass  vessel  in 
which  the  mixture  is  made.  It  is  possible  however  to  obtain  the  acid  in  a 
liquid  state,  and,  therefore,  its  separate  existence  is  well  established(lQ) 
As  I  have  before  indicated,  our  experiments  with  it  will  be  all  made  with  its 
salts. 

I  mix  a  few  grains  of  loaf  sugar  in  powder,  with  about  half  its  quantity  of 
the  chlorate  of  potassa,  and  touch  the  mixture  with  a  drop  of  sulphuric  acid. 

Emily,  Its  combustion  was  nearly  like  that  of  gunpowder,  only  some- 
what more  slow.  The  chloric  acid  was  in  this  case  decomposed  by  the 
sulphuric,  and  the  combustion  effected  by  the  liberated  oxygen;  was  it  not 
so(20)? 

J\frs  B-  Undoubtedly.  Heat,  you  know,  will  cause  nitre  to  part  with  a 
large  portion  of  its  oxygen,  but  from  the  chlorate  of  potassa  this  gas  is  ob- 
tained in  much  larger  quantity,  and  in  a  state  of  greater  purity.  To  this 
material  the  chemist  resorts  whenever  he  has  occasion  to  employ  oxygen 


14.  What  is  the  rationale  of  its  formation? 

15.  What  objection  is  ui-ged  against  this  explanation? 

16.  By  what  reasoning  is  this  objection  obviated? 

17.  How  is  the  salt  obtained  in  the  crystalline  form? 

18.  What  strong  resemblance  is  there  between  this  chlorate  and  nitre? 

19.  What  takes  place  when  sulphuric  acid  is  poured  upon  this  salt? 
$0?  What  experiment  may  be  performed  with  the  chlorate  and  sugar? 


ON  CHLORATE  OF  POT  ASS  A.  245 

gas  in  its  most  perfect  form.  One  hundred  grains  of  the  chlorate  afford  about 
twenty-five  grains  of  the  gas,  or,  in  bulk,  about  seventy  «-nve  cubic  inches(21). 

Caroline.  The  famous  match-lights,  which  I  have  so  often  used,  must,  I 
think,  depend  upon  this  chlorate  for  their  action. 

•Mrs  B.  Entirely;  these  matches,  after  being  covered  with  sulphur,  are 
dipped  into  a  mixture  of  chlorate  of  potassa,  sugar,  and  sulphur,  made  into  a 
paste  with  gum  water.  They  are  then  dried,  and  when  touched^with  sul- 
phuric acid,  instantaneously  inflame. 

Caroline.  The  phial  then,  into  which  we  dip  them  must  contain  sulphuric 
acid(22).  But  what  causes  it  to  get  out  of  ordei*,  as  it  very  soon  does? 

Mrs  B.  The  sulphuric  acid,  by  the  frequent  opening  of  the  phial,  at- 
tracts moisture  from  the  atmosphere,  and  thus  becomes  too  much  diluted 
to  produce  the  intended  effect.  £*/ 

By  the  aid  of  sulphuric  acid,  the  chlorate  may  be  made  to  give  out  its 
oxygen  under  water,  and  if  this  takes  place  in  contact  with  phosphorus,  its 
combustion  will  be  effected.  At  the  bottom  of  this  glass  of  water  are  some 
small  pieces  of  phosphorus,  covered  with  some  of  the  salt;  I  pour  some 
strong  sulphuric  acid  down  the  side  of  the  glass,  and  the  combustion  com- 
mences the  moment  the  acid  touches  the  chlorate(23). 

Emily.  How  wonderful  it  is  to  see  flame  bursting  out  under  water,  and 
how  gratifying  to  be  able  to  account  for  it  !  We  know'  now,  through 
your  kind  instructions,  that  the  sulphuric  acid  decomposes  the  salt,  by  com- 
bining with  its  potash,  and  that  the  disengaged  oxygen  effects  the  combus- 
tion of  the  phosphorus. 

Mrs  B.  Very  well  explained;  and  with  a  little  more  reflection  you 
would  have  added,  that  the  increase  of  temperature  resulting  from  the  mix- 
ture of  the  sulphuric  acid  and  water,  powerfully  aids  in  promoting  the  com- 
bustion(24). 

Friction,  or  a  blow,  will  enable  many  combustibles  to  decompose  this 
chlorate.  Observe,  1  put  two  or  three  grains  of  the  salt,  and  about  half  the 
quantity  of  flowers  of  sulphur  into  this  iron  mortar;  now  I  will  rub  them  to- 
gether, with  the  pestle. 

Caroline.  Astonishing!  what  a  succession  of  reports;  they  sound  like  a 
number  of  pistols  fired  one  after  another(25). 

Mrs  B.  If  I  mix  the  pulverized  chlorate  and  the  sulphur  intimately  to- 
gether, then  collect  the  mixture  in  a  heap  in  the  mortar,  and  strike  it  with 
the  pestle,  the  report  will  be  like  that  of  a  gun.  Most  of  the  metals,  mixed 
with  the  chlorate,  in  the  form  of  filings,  and  treated  in  the  same  way,  will 
also  produce  explosions.  Charcoal,  likewise,  when  in  powder  and  thus 
mixed,  is  inflamed,  either  by  friction,  or  by  a  blow.  Its  action,  however,  is 
less  violent  than  that  of  sulphur,  or  the  metals(26). 

Caroline.  Might  not  a  gunpowder  much  stronger  than  that  m  use  be  pro- 
duced by  employing  the  chlorate  of  potassa,  instead  of  nitre? 

Mrs  B.  Yes:  and  this  has  been  actually  attempted;  but  several  indi- 
viduals lost  their  lives  from  the  explosion  of  the  materials  whilst  they  were 
being  mixed  together(27). 

Emily.  The  powder  now  used  produces  so  much  desolation,  that  we 
need  not  regret  the  difficulty  of  preparing  such  a  kind  as  would  be  still 
more  destructive. 


21.  What  is  said  on  the  procuring  oxygen  from  the  chlorate  of  potassa? 

22.  How  are  the  match-lights  prepared  from  this  salt? 

23.  How  may  phosphorus  be  made  to  burn  under  water  by  its  aid? 

24.  In  what  way  is  this  phenomenon  explained? 

25.  When  the  chlorate  is  rubbed  up  with  sulphur,  what  ensues? 

26.  What  explosions  are  mentioned  as  produced  by  its  aid? 

27.  Has  it  been  attempted  to  use  it  instead  of  nitre,  in  gunpowder? 

V  2 


246  CONVERSATIONS  ON  CHEMISTRY. 

J\frs  B.  A  kind  of  powder  which  inflames  by  a  blow,  instead  of  by 
flint  and  steel,  and  called  percussion  po-iodei*,  has  been  made  by  substituting 
the  chlorate  for  the  nitrate  of  potassa.  This  powder  was,  for  awhile,  em- 
ployed for  the  priming  of  percussion  guns;  but  fulminating  mercury  (p.  197) 
is  now  generally  used  for  that  purpose,  it  having  been  found  to  be  much 
better  adapted  to  the  purpose  than  the  former(28). 

After  having  thus  explained  to  you  the  properties  of  the  hyperoxymuriate, 
or  chlorate  of  potassa,  I  shall  not  introduce  the  other  alkaline  and  earthy  chlo- 
rates, because  they  are  so  analogous  in  their  general  properties  as  not  to 
offer  any  thing  which  would  be  particularly  interesting  to  you.  We  have  yet, 
however,  something  to  say  respecting  the  muriates  and  chlorides,  and  will  in 
the  first  place  recur  to  that  with  which  you  are  already  the  best  acquainted; 
I  mean  the  MURIATE  OF  SODA. 

Caroline.  Your  injunction  at  the  commencement  of  our  conversation  to- 
day, leads  us  to  anticipate  some  difficulty  as  regards  the  constitution  of  this 
salt,  but  with  your  aid  we  may  confidently  hope  that  we  shall  not  find  it 
insurmountable. 

Jlfrs  B.  The  received  doctrine  as  regards  muriate  of  soda  is,  that,  in  a 
perfectly  dry  state,  what  we  call  by  that  name,  is  really  a  CHLORIDE  OF  SO- 
DIUM; that  when  this  chloride  is  dissolved  in  water,  it  is,  in  the  mere  act 
of  solution,  converted  into  muriate  of  soda;  and  that  if  the  water  be  again 
evaporated,  the  muriate  of  soda  is  then  decomposed,  and  chloride  of  sodium 
reproduced(29).  I  need  not  inform  you  what  is  the  chemical  difference  be- 
tween those  two  compounds. 

Emily.  That  I  think  we  understand  perfectly.  The  chloride  of  sodium 
consists  of  metallic  sodium,  united  to  chlorine,  and  it  contains  nothing 
therefore  but  these  two  substances;  but  the  muriate  of  soda  is  composed 
of  the  oxide  of  sodium  (common  soda)  combined  with  muriatic  acid,  which^ 
on  its  part,  consists  of  hydrogen  and  chlorine.  Muriate  of  soda,  therefore, 
contains  sodium,  chlorine,  oxygen,  and  hydrogen(30). 

Caroline.  I  shall  require  some  unequivocal  testimony,  before  I  have  per- 
fect faith  in  these  sudden  and  imperceptible  transitions. 

JMrs  B.  Pure  metallic  sodium  burns  very  readily  in  chlorine;  and  when 
its  combustion  is  effected  -without  the  presence  of  any  moisture  -whatever, 
the  product  is  identical  with  common  salt.  Can  this,  therefore,  which  con- 
tains neither  oxygen  nor  hydrogen,  be  a  muriate  of  soda? 

Emily.  Assuredly  not,  because  neither  of  the  constituents  of  water  is 
present,  or  concerned  in  the  process.  It  seems  plain  that  you  can,  in  this  . 
case,  obtain  nothing  but  the  chloride  of  sodium(3\.). 

Mrs  B.  Yet,  when  you  dissolve  this  chloride  of  sodium  in  water,  if  you 
pour  sulphuric  acid  into  the  solution,  muriatic  acid  will  be  expelled,  and 
sulphate  of  soda  formed.  It  appears,  therefore,  necessarily  to  follow,  that 
when  the  chloride  of  sodium  comes  into  contact  with  water,  this  fluid  is  de- 
composed, that  the  sodium  becomes  soda  by  combining  with  its  oxygen,  and 
that  the  chlorine  becomes  muriatic  acid  by  combining  with  its  hydrogen. 
When  the  Miater  is  evaporated,  the  hydrogen  and  the  oxygen  are  expelled,  \ 
and  being  presented  to  each  other  in  their  nascent  state,  again  unite,  and 
form  water,  whilst  the  sodium  and  the  chlorine  are  also  restored  to  their 
former  state(32). 

Caroline.  Such  evidence  certainly  "  must  give  us  pause,"  and  induce  us 
to  study  this  particular  subject  with  great  care. 


28.  Of  what  does  the  priming  of  percussion  guns  consist? 

29.  What  is  the  received  opinion  respecting  muriate  of  soda? 

30.  In  what  respects  do  muriate  of  soda,  and  chloride  of  sodium  differ? 

31.  What  proof  is  given  that  common  salt,  when  dry,  is  a  chloride? 

32.  What  shows  that  it  becomes  a  muriate  by  solution? 


ON  THE  MURIATES.  247 

J\frs  B.  Dismissing,  for  a  while,  our  theoretical  discussion,  and  return- 
ing to  truths  of  a  more  palpable  kind,  we  will  say  something  upon  the  na- 
tural history  of  this  most  common,  and  most  valuable  of  all  the  saline  com- 
pounds. 

Muriate  of  soda  is  principally  obtained  from  sea- water,  either  by  natural 
or  artificial  evaporation,  but  it  is  seldom  perfectly  pure,  as  a  number  of 
-otlier  salts  exist  in  the  ocean,  some  of  which  are  bitter  and  deliquescent. 
Sometimes  a  considerable  portion  of  these  foreign  salts  is  allowed  to  remain 
with  the  muriate  of  soda,  in  which  case  they  not  only  injure  its  taste,  but 
cause  it  to  attract  moisture,  and  thereby  render  it  unfit  for  preserving  meat 
or  fish.  These  foreign  salts  are  principally  the  muriates  of  magnesia  and 
of  lime,  and  the  sulphates  of  magnesia  and  of  soda(33). 

Caroline.  But  all  the  salt  of  our  tables  is  not  derived  from  the  sea,  as 
there  are  immense  mines  of  it,  and  a  great  number  of  salt  springs  in  the 
interior  of  many  countries.  I  recollect  an  account  of  a  mine  in  Poland 
which  has  been  worked  for  centuries,  and  which  runs  to  a  great  distance 
underground,  with  columns,  houses,  churches,  and  other  establishments,  all 
cut  out  of  the  solid  salt,  and  glistening  with  surprising  brilliancy,  from  re- 
flecting the  light  of  the  lamps  and  torches  which  the  miners  are  compelled 
constantly  to  burn(34). 

Mrs  B.  Salt,  from  its  great  value  to  man,  has  been  adopted  as  the  em- 
blem of  every  thing  that  is  excellent  and  worthy,  in  the  human  character; 
and  a  benevolent  Providence  has  diffused  it  through  countries  remote  from 
the  ocean,  by  the  formation  of  mountains,  mines,  lakes  and  springs,  from 
which  this  necessary  substance  may  be  obtained. 

Its  uses  are  numerous;  it  preserves  for  years  those  perishable  animal  sub- 
stances which,  without  it,  could  not,  sometimes,  be  kept  for  a  single  day.  It 
.  not  only  heightens  the  flavour  of  our  food,  but  contributes  to  health  by  pro- 
moting digestion  and  nutrition.  Our  domestic,  and  other,  animals  have  a 
natural  fondness  for  it,  and  derive  advantage  from  its  use.  To  the  arts  it 
supplies  muriatic  acid,  sulphate  of  soda,  carbonate  of  soda,  chlorine  and 
chlorides  for  bleaching.  It  is  employed  in  the  manufacturing  of  calomel, 
and  other  chemicals;  the  potter  applies  it  to  the  glazing  of  certain  kinds  of 
earthenware;  and  the  physician  administers  it  as  a  remedy  in  certain  dis- 
eases, and  destroys  contagion  by  liberating  its  chlorine(35). 

Emily.     The  article  which  you  have  just  placed  upon  the  table,  with  the 

.  label  of  sal  ammoniac  is  not  quite  a  stranger  to  us,  as  you  used  it  in  the 

preparation  both  of  ammonia  and  of  its  carbonate:  you  also  gave  us  some 

account  of  its  origin,  and  of  the  means  by  which  it  is  manufactured  (p.  169). 

Mrs  B.  You  are  fully  aware  that  its  proper  chemical  name  is  the  MU- 
RIATE OF  AMMONIA.  My  principal  reason  for  introducing  it  now,  is  to 
exhibit  its  formation  by  the  mere  mixture  of  gaseous  muriatic  acid  and  am- 
monia: the  moment  they  come  in  contact  with  each  other,  their  bases  will 
combine,  and  form  the  solid  salt.  I  employ  for  this  purpose  the  same 
apparatus  which  was  used  in  preparing  the  carbonate  of  ammonia  (p.  171). 

Caroline.  I  recollect  being  much  interested  in  that  experiment,  as 
evincing,  in  a  very  striking  manner,  the  effect  of  chemical  combination  in 
changing  the  form  of  bodies  ;  two  gases  being  instantaneously  brought  into 
the  solid  state. 

Mrs  B.  And  in  the  present  instance  the  change  is  still  more  remarka- 
ble, as  both  the  ammonia  and  the  muriatic  acid  possess  an  extremely  pun- 
gent odour,  which  is  entirely  lost  in  their  state  of  combination,  which,  you 
know,  is  not  the  case  with  the  carbonate  of  ammonia. 


33.  What  salts  does  sea- water  contain,  hesides  the  muriate  of  soda? 

34.  From  what  other  sources  is  common,  salt  procured? 

35.  Enumerate  some  of  the  uses  of  this  substance 


248  CONVERSATIONS  ON  CHEMISTRY. 

Formation  of  Muriate  of  Ammonia,  or  Sal  Ammoniac. 
c, 


la  the  flask  (A),  I  have  some  dry  slaked  lime,  mixed  with  muriate  of 
ammonia.  This,  upon  the  application  of  a  moderate  heat,  will  supply  am- 
monia. In  the  other  flask  (B),  there  is  common  salt,  upon  which  I  pour 
sulphuric  acid,  and  the  gaseous  muriatic  acid  will  immediately  escape. 
You  perceive  that  when  the  two  gases  come  into  contact,  in  the  receiver 
(C),  snow-white  clouds  are  produced,  and  eventually  the  solid  salt  will 
form  an  incrustation  upon  the  inside  of  the  glass  globe(36). 

In  this  combination  much  heat  is  disengaged,  a  fact  for  which,  I  have  no 
doubt,  you  can  readily  account. 

Caroline.  We  must  undoubtedly  ascribe  the  production  of  heat  to  the 
condensation  of  the  two  gases,  which  pass  into  the  solid  state,  and  conse- 
quently part  with  their  latent  heat;  for  although  there  are  some  exceptions 
to  the  law  that  heat  is  given  out  when  fluids  become  solids,  and  is  rendered 
latent  when  solids  assume  the  fluid  form,  yet  these  effects  are  so  general  as  to 
justify  us  in  resorting  to  it  for  an  explanation  of  these  phenomena^).,,. 

Mrs  B.  I  am  gratified  at  the  cautious  manner  in  which  you  give  your 
explanation,  as  it  is  in  accordance  with  the  true  spirit  of  inquiry  upon  such 
subjects.  We  must  now  dismiss  sal  ammoniac,  with  a  concise  view  of 
some  of  the  useful  purposes  to  which  it  is  applied.  It  is  employed  as  a 
flux  in  the  soldering  of  certain  metals  together,  and  in  the  process  of  tin- 
ning; that  is,  the  covering  of  iron  or  copper  with  a  coat  of  tin,  in  order  to 
protect  these  metals  from  oxidation.  In  the  art  of  dyeing  it  is  used  to  mo- 
dify and  give  brightness  to  certain  colours.  It  is  said  also  that  the  manufac- 
turer of  snuff  sometimes  adds  the  muriate  of  ammonia  to  his  pulverized 
tobacco  to  increase  its  pungency.  In  the  laboratory  of  the  chemist  it  sup- 
plies the  volatile  alkali,  when  it  is  wanted  either  in  its  pure  state,  or  as  a 
base  to  other  salts(38). 

Emily.  In  procuring  ammonia  from  its  muriate  by  means  of  lime,  a  large 
quantity  of  muriate  of  lime  must  be  formed.  Is  this  salt  of  any  use? 

Mrs  B.  MURIATE  OF  LIME  is  one  of  the  most  deliquescent  of  the  salts: 
indeed  it  so  eagerly  attracts  moisture,  that  when  exposed  to  the  atmos- 
phere, it  quickly  assumes  the  liquid  form.  If  wanted  in  a  dry  state,  it  must 
therefore  be  closely  stopped  up.  It  is  used  by  the  chemist  in  his  researches, 
in  order  to  deprive  gases  and.  other  substances  of  their  moisture;  and  it  forms 
an  ingredient  in  frigorijic  mixtures.  The  physician  also  sometimes  em- 
ploys it  as  a  medicine. 

Muriate  of  lime  is  one  of  the  salts  contained  in  sea-water,  and  if  not  per- 


36.  How  may  sal  ammoniac  be  formed  from  its  constituents' 

37.  How  do  you  account  for  the  extrication  of  heat  in  this  process? 

38.  To  what  uses,  in  the  arts,  is  sal  ammoniac  applied? 


ON  THE  CHLORIDE  OF  LTME.  249 

tcctly  separated  from  common  salt,  communicates  to  it  the  bitter  taste,  and 
the  tendency  to  deliquesce,  already  noticed(39).  The  list  of  the  uses  of 
this  salt  is  a  short  one,  but  when  the  muriatic,acid  is  deprived  of  its  hydro- 
gen and  its  remaining  constituent  combined  with  lime,  we  obtain  a  compound 
of  much  greater  importance. 

Emily.      That  then  must  be  chloride  of  lime. 

Jlfrs  B.  I  was  convinced  that  you  would  name  it  at  once.  CHLOHIBK 
OF  I.IXE  and  chlorate  of  lime  are  not  unfrequently  confounded  together: 
you,  however,  are  fully  aware  of  the  difference  between  them.  Chloride 
of  lime  may  be  obtained  in  solution  by  passing  chlorine  into  a  vessel  con- 
taining slaked  lime  and  water,  but  it  is  now  uniformly  procured  for  use  m 
the  arts  by  causing  the  gas  to  pass  into  vessels,  or  chambers,  containing  dry 
slaked  lime  in  powder.  The  chlorine,  in  this  case,  combines  with  the 
lime,  and  converts  it  into  a  chloride.  This  article  is  manufactured  to  a 
great  extent  both  in  Europe  and  in  this  country(40). 
Caroline.  And  what  are  its  particular  uses? 

Jtfrs  JB.  They  are,  principally,  two:  it  is  employed  in  bleaching,  and  as 
a  disinfecting  agent.  Chlorine,  you  know,  is  itself  soluble  in  water;  but  when 
this  aqueous  solution  was  used  in  bleaching,  the  gas  which  escaped  was 
found  to  be  extremely  injurious  to  the  workmen.  The  chloride  of  lime 
is  also  soluble  in  water;  and  this  solution  produces  its  bleaching  effects 
without  the  disengagement  of  gaseous  chlorine(4l).  In  bleaching  by  the 
aid  of  chlorine,  the  oxygen  of  the  water  is  undoubtedly  the  agent  which  dis- 
charges the  colouring  matter;  and  although  something  has  been  already  said 
respecting  its  disengagement  and  action  through  the  medium  of  chlorine,  it 
•is  one  of  those  processes  the  explanation  of  which  may  well  bear 
repetition. 

Caroline.  Indeed,  my  dear  madam,  I  shall  be  much  obliged  to  you  for 
sucti  a  repetition;  for  I  find  that  I  always  learn  more  in  a  recapitulation,  than 
I  do  in  the  first  explanation  of  any  principle. 

Mrs  B.  When  goods  were  bleached  by  the  old  process  of  exposure 
to  the  air,  to  light,  and  to  moisture,  oxygen  was  confessedly  the  active  agent 
in  discharging  the  colouring  matter,  and  its  operation  was  so  slow  as  some- 
times to  require  months  for  its  completion;  but  by  the  chemical  process, 
oxygen  is  applied  in  its  nascent  state,  and  the  bleaching  is  effected  in  a  few 
days,  and  sometimes  even  in  a  few  hours. 

When  dissolved  in  water,  the  chloride  of  lime  is  gradually  converted 
into  a  muriate  of  lime;  for  the  chlorine,  abstracting  hydrogen  from  the  water, 
becomes  muriatic  acid,  and,  in  this  new  form,  unites  again  to  the  lime.  The 
nascent  oxygen  of  the  decomposed  water  combines  with  the  colouring  mat- 
ter, renders  it  soluble,  and  therefore  easy  to  be  removed(42).  The  differ- 
ence in  time  which  the  two  modes  require  is  very  great,  but  the  theory  of 
the  action  of  oxygen  is  the  same,  whether  supplied  by  the  atmosphere  or 
by  water. 

Emily.  This  use  of  chlorine  is  indeed  a  valuable  present  from  chemis- 
try to  the  arts;  and  if  it  is  as  efficacious  in  destroying  contagion,  as  it  is  in 
discharging  colours,  science  has  triumphed  over  one  of  the  greatest  evils  to 
•which  human  nature  is  subjected. 

JMrs  B.      The  power  of  chlorine  in  destroying  offensive  odours,  and  in 
neutralizing  infectious  effluvia,  has  been  known  for  a  considerable  length  of 
'time;  but  the  plan  formerly  pursued  was  to  disengage  the  gas  in  large  quan- 
tities, and  to  admit  of  this,  it  was  necessary  to  remove  the  occupants  of  the 


39.  How  is  muriate  of  lime  formed,  and  what  are  its  properties? 

40.  By  what  means  is  the  chloride  of  lime  produced? 

41.  In  what  manner  is  this  chloride  used  in  bleaching? 

42.  What  is  the  theory  of  its  action  in  producing  this  effect? 


250  CONVERSATIONS  ON  CHEMISTRY. 

apartments  to  be  disinfected,  and  to  close  them  for  a  considerable  length  of 
time.  The  chloride  of  lime,  however,  performs  its  office  without  requiring 
any  such  precaution. 

Caroline.  Every  man,  woman  and  child  ought  to  be  made  acquainted 
with  a  process  so  very  beneficial,  and  so  frequently  needed. 

Mrs  B.  The  chloride  of  lime  is  now  kept  by  the  apothecaries,  and  is  a 
rfieap  article.  It  may  be  made  ready  for  use  when  wanted  by  dissolving 
four  ounces  of  it  in  a  pint  of  water.  A  wine  glass  full  of  this  solution  added 
to  three  quarts  of  water,  or  one  part  in  forty,  will  effectually  remove  the 
effluvia  arising  from  animal  or  vegetable  putrefaction.  In  hospitals,  ana- 
tomical rooms,  and  similar  places,  the  solution  may  be  sprinkled  about, 
and  will  rapidly  purify  the  atmosphere(43).  The  smell  of  bilge  water  on 
board  of  ships,  that  of  paint  in  newly  painted  rooms,  and  the  offensive  odours 
arising  from  various  causes,  are  in  this  way  not  merely  removed,  but  their 
sources  also  purified.  In  cellars,  and  similar  places,  a  portion  of  the 
dry  powder  may  be  thinly  scattered  upon  the  floor,  and  the  same  may  be 
done  with  the  most  perfect  success  in  those  manufactories  which  are  un- 
healthy and  offensive(44). 

Emily.  How  delightful  and  ennobling  are  such  discoveries!  But  I  am 
at  a  loss  to  perceive  by  what  agency  the  chlorine  is  disengaged  from  the 
lime,  as  there  is  no  acid  added  to  dislodge  it. 

Mrs  B.  It  appears  that  the  carbonic  acid  which  is  always  disengaged 
with  putrid  effluvia,  is,  of  itself,  sufficient  for  that  purpose.  It  combines 
with  the  lime,  converts  it  into  a  carbonate,  and  thus  expels  the  chlorine,  but 
so  gradually  as  scarcely  to  allow  its  odour  to  be  perceived(45). 

I  have  now  placed  before  you  the  most  important  of  the  combinations  of 
chlorine,  with  the  exception  of  aqua  regia,  and  of  those  substances  formed 
by  the  union  of  chlorine  with  mercury;  but  I  must  not  dismiss  the  subject 
without  saying  something  of  each  of  these.  That  which  relates  to  mercury 
was  purposely  omitted  when  we  treated  of  the  metals,  because  you  were 
then  unacquainted  with  chlorine. 

Caroline.  I  recollect  your  telling  us  that  aqua  regia,  was  by  the  che- 
mist called  NITEO-MTJHIATIC  ACID,  and  that  it  was  the  only  acid  capable  of 
dissolving  gold  or  platinum. 

Mrs  B.  NITHO -MURIATIC  ACID  is  produced  by  merely  mixing  nitric 
and  muriatic  acids  together;  and  the  effect  of  this  mixture  will  be  shown  by 
an  easy  experiment,  which  I  have  once  performed,  and  will  now  repeat(46). 

I  have  here  two  wine  glasses;  into  each  I  put  a  leaf  of  gold:  I  now  pour 
nitric  acid  on  one  of  the  leaves,  and  muriatic  acid  on  the  other.  The  gold 
you  perceive  remains  unchanged:  it  will  soon  disappear,  however,  if  I  pour 
the  contents  of  the  two  glasses  together(47). 

Emily.  It  has  already  dissolved,  not  a  vestige  being  left:  the  acids  also 
appear  of  a  much  deeper  colour,  and  emit  a  stronger  odour  than  they  did 
before  their  mixture. 

Mrs  B.  Gold  leaf,  when  immersed  in  a  vessel  of  gaseous  chlorine,  com- 
bines v  ith  it,  and  is  converted  into  a  chloride,  and  in  the  present  instance, 
also,  chlorine  is  the  agent  which  dissolves  the  gold.  You  have  seen  that 
neither  the  nitric  nor  muriatic  acid  alone  will  produce  this  effect(48). 

Caroline.     But  the  chlorine  is  already  combined  with  hydrogen  to  form 


43.  How  is  it  used  as  a  disinfecting  agent? 

44.  What  is  remarked  respecting  the  effects  produced  by  it? 

45.  How  is  the  chlorine  liberated  in  these  cases? 

46.  How  is  aqua  regia,  or  nitro-muriatic  acid,  formed? 

47.  By  what  experiment  is  the  power  of  this  acid  shown? 

48.  What  appears  to  be  the  solvent  of  the  gold? 


ON  THE  CHLORIDES  OF  MERCURY.  251 

muriatic  acid,  and  if  the  gold  decomposed  the  acid  and  combined  with  its 
chlorine  we  ought  to  obtain  hydrogen  gas. 

Mrs  B.  It  is  the  oxygen  of  the  nitric  acid,  and  not  the  gold  which  dis- 
engages the  chlorine.  When  the  two  acids  are  poured  together,  a  part  of  the 
oxygen  of  the  nitric  acid  combines  with  the  hydrogen  of  a  portion  of  the 
muriatic  acid,  and  the  latter,  of  course,  becomes  chlorine,  whilst  the  for- 
mer is  reduced  from  the  state  of  nitric,  to  that  of  nitrous  acid.  This  acid  and 
chlorine  are  consequently  disengaged,  and  it  is  from  these  that  the  colouring 
of  the  nitro-muriatic  acid  and  the  red  fumes  proceed.  The  chlorine  which 
is  liberated  dissolves  the  gold(49). 

If  after  mixing  the  two  acids,  we  were  to  heat  them  sufficiently  to  expel 
the  nitrous  acid  and  the  chlorine,  the  remaining  acid  would  have  no  power 
to  act  upon  gold. 

I  will  now  briefly  explain  to  you  the  formation  of  corrosive  sublimate, 
and  of  calomel,  which  are  both  CHLORIDES  OF  MERCURY:  there  is,  however, 
this  difference  between  them,  the  quantity  of  chlorine  contained  in  corro- 
sive sublimate  is  twice  as  great  as  that  in  calomel.  The  latter  is  the  chloride 
of  mercury;  the  former  (corrosive  sublimate),  the  bichloride,  or  perchloride, 
of  mer  cur  y(  5  0  ). 

Emily.  These  then  afford  another  instance  of  a  great  change  of  proper- 
ties by  merely  changing  the  proportions  of  the  component  parts  of  a  body. 
Corrosive  sublimate  is,  we  know,  a  most  virulent  poison,  whilst  calomel 
is  safely  used  as  a  medicine  in  considerable  quantities. 

Mrs  B.  Mercury,  when  sufficiently  heated,  undergoes  combustion  in  chlo- 
rine, burning  with  a  pale  red  flame;  the  product  being  the  perchloride  of  mer- 
cury, or  corrosive  sublimate(51).  This  perchloride  may  be  converted  into 
protochloride  of  mercury,  or  calomel,  by  rubbing  it  in  a  mortar  with  about  its 
own  weight  of  metallic  quicksilver.  The  two  substances  will  combine  together, 
each  atom  of  chlorine  taking  to  itself  an  atom  of  mercury,  and  the  union  is 
completed  by  sublimation.  This  is  not  the  process  by  which  these  pre- 
parations are  manufactured,  but  it  serves  to  give  a  direct  view  of  their  com- 
position(52). 

Caroline.  You  have  several  times  spoken  of  the  analogy  between  chlo- 
rine and  oxygen,  and  I  have  sometimes  wondered  at  their  not  having  been 
treated  of  together;  but  the  delay  in  introducing  chlorine  no  longer  surpri- 
ses me,  as  its  combinations  and  changes  render  its  chemical  history  an  ex- 
tremely difficult  subject  to  comprehend,  and  one  which  would  therefore 
have  been  a  complete  blank  to  us  at  an  earlier  period. 

Mrs  B.  But  few  doctrines  in  chemistry  have  encountered  greater  op- 
position than  that  of  the  simple  nature  of  chlorine;  and  at  the  time  when 
the  name  of  oxymuriatic  acid  was  changed  to  that  of  chlorine,  chemists 
were  not  acquainted  with  any  other  substance,  excepting  oxygen,  which  sup- 
ported combustion.  Two  have,  however,  been  subsequently  discovered 
which  appear  to  be  simple,  and  are  so  analogous  to  chlorine  in  their  gene- 
ral properties,  as  powerfully  to  sustain  its  claim  to  be  considered  as  a  sim- 
ple or  elementary  body.  These  two  substances  are  Iodine  and  Bro- 


Emily.  This  discovery  must  have  been  very  gratifying  indeed  to  the 
founders  and  advocates  of  the  new  theory. 

Mrs  JB.  IODINE  is  a  solid,  which  is  obtained  in  minute  scales,  or  grains, 
of  a  bluish-black  colour,  and  a  metallic  lustre.  It  is  so  friable  as  to  be 


49.  By  what  reaction  is  the  chlorine  disengaged? 

50.  What  are  corrosive  sublimate  and  calomel  ? 

51.  How  may  the  direct  formation  of  corrosive  sublimate  be  effected? 

52.  How  may  this  be  converted  into  the  protochloride  or  calomel? 

53.  What  discoveries  lend  aid  to  the  theory  of  the  simple  nature  of 
chlorine? 


252  CONVERSATIONS  ON  CHEMISTRY. 

easily  bruised  between  the  fingers.  It  volatilizes,  though  slowly,  at  com- 
mon temperatures.  When  moderately  heated,  it  is  converted  into  a  va- 
pour of  a  rich  violet  colour.  I  have  some  grains  of  it  closed  up  in  this 
flask,  which  I  will  heat  by  holding  it  over  the  lamp,  turning  it  about  to 
warm  it  equally(54). 

Caroline.  You  may  indeed  call  that  a  rich  colour,  I  think  it  the  most 
splendid  purple  I  have  ever  witnessed. 

Mrs  B.  Its  name  is  derived  from  a  Greek  word  indicative  of  its  colour. 
Like  chlorine,  its  principal  source  is  the  ocean,  as  it  is  generally  procured 
from  the  ashes  of  sea  weeds,  although  found  in  some  other  combinations. 
Its  odour  is  very  similar  to  that  of  chlorine,  which  it  resembles  in  being  acrid 
and  corrosive.  In  its  affinities  also  it  is  strikingly  similar,  decomposing  wa- 
ter and  forming  with  its  hydrogen  a  gaseous  acid,  called  hydriodic  acid  gas. 
With  oxygen  it  produces  iodic  acid,  and  with  chlorine  chloriodic  acid.  It 
combines  with  nitrogen,  furnishing  an  explosive  iodide  of  nitrogen;  and  the 
parallel  between  it  and  chlorine  might  be  extended  through  nearly  all  its 
combinations(55). 

Emily.  Under  what  circumstances  does  iodine  appear  to  be  a  supporter 
of  combustion? 

•Mrs  B.  Its  agency  as  a  supporter  of  combustion  is  very  limited.  Po- 
tassium, and  a  few  other  substances,  however,  burn  in  it  with  the  usual  ap- 
pearances; and  its  combinations  with  bases  generally,  are  analogous  to 
those  produced  by  the  acknowledged  supporters  of  combustion(56). 

Caroline.  If  bromine  bears  as  strong  a  likeness  to  chlorine  as  iodine  does, 
they  certainly  must  be  allowed  to  form  a  well  characterized  class. 

Mrs  B.  The  similarity  is  so  great,  that  its  discoverer  thought  it  proba- 
ble that  bromine  was  a  compound  of  chlorine  and  iodine.  Upon  the  most 
careful  investigation,  however,  its  character  as  a  simple  substance  appears 
to  be  well  established(57). 

BROMINE  is  a  fluid  of  a  blackish-red   colour.     It  is  volatile,  and  when 
volatilized,  its  vapour  is  of  a  bright  red,  resembling  that    of  nitrous  acid. 
It  is  found  in  the  waters  of  the  sea  and  of  saline  springs,  and  also  in  those 
sea  weeds   which    contain    iodine.     It  combines  both  with  hydrogen  and 4 
with  oxygen,  forming  acids  which  possess  nearly  the  same  affinities  with"" 
those  formed  by  iodine  and  chlorine  with  the   same  principles.      Potas- 
sium, tin,  and  antimony  burn  in  it,  and  are  converted  into  bromides.     Like 
its  congeners,  it  has  resisted  every  attempt  at  decomposition(58). 

Oxygen,  chlorine,  iodine,  and  bromine  are  the  only  undecompounded 
bodies  which  are  electro-negative,  and  which  consequently  pass  to  the 
positive  pole  when  placed  in  the  voltaic  circuit. 

Emily.  This  last  character  seems,  by  a  very  peculiar  resemblance,  to 
unite  these  four  substances  together,  as  belonging  to  one  family.  All  the 
other  simple  bodies,  numerous  as  they  are,  are  carried  by  their  electric 
state,  to  the  negative  pole  of  the  voltaic  battery,  whilst  these  stand  alone,  as 
being  carried  to  the  positive  pole(59). 

Mrs  B.  Before  finally  parting  with  bromine  and  iodine,  I  ought  to  in- 
form you  that  the  latter  has  been  advantageously  applied  in  the  arts  as  the 
foundation  of  some  very  brilliant  colours,  particularly  in  the  printing  of 
calicos.  It  has  also  taken  a  place  in  the  materia  medica,  as  an  article 

54.  What  appearances  are  exhibited  by  iodine? 

55.  Whence  is  it  obtained,  and  what  are  its  resemblances  to  chlorine? 

56.  In  what  instances  is  it  a  supporter  of  combustion? 

57.  What  proves  the  resemblance  between  iodine  and  bromine? 

58.  What  is  said  of  the  appearance  and  combinations  of  bromine? 

59.  What  special  character  unites  oxygen,  chlorine,   iodine,  and  bro- 
mine ? 


ON  SALTS.  253 

acting  more  directly  and  powerfully  on    the  absorbents  than  any  other  in 
the  whole  list  of  remedial  applications(60). 


CONVERSATION  XXV. 

ON  THE  GENERAL  PROPERTIES  OF  SALTS. 

Of  -what  a  Salt  must  consist.  What  -were  formerly  called  Salts.'  Sa- 
pidity of  Salts  dependent  upon  their  Solubility.  Circumstances  -which 
control  the  Solubility  of  a  Salt.  Deliquescence,  Efflorescence,  and  Per- 
manence. Water  of  Crystallization.  Anhydrous  Salts.  Effect  of  hot 
Water  in  dissolving  Salts.  Formation  of  Regular  Crystals.  Ttvo  So-lid 
Salts  rendered  Jluid  by  Mixture.  Incompatible  Salts.  Separation  of 
Salts  from  each  other.  Salts  dissolved  in  a  saturated  Solution.  Double 
Salts.  Definition  of  a  Crystal.  Some  Crystals  not  inutable  by  art. 

Mrs  B.  In  our  conversations  upon  the  elementary  principles  of  bodies, 
and  of  the  compounds  which  they  form  by  their  union,  you  have  become 
acquainted  with  a  considerable  number  of  that  large  class  of  substances 
which  the  chemist  denominates  SALTS.  There  are,  however,  some  facts 
in  regard  to  this  very  important  class  of  bodies  which  have  been  but  briefly 
noticed,  and  others  that  have  not  been  even  hinted  at:  these  will  form  the 
subject  of  our  inquiries  to-day.  You  undoubtedly  recollect  the  general 
constitution  of  a  salt. 

Caroline.  Perfectly,  I  believe.  Salts  are  substances  which  consist  of 
an  acid  united  to  a  base(l). 

Mrs  S.  The  term  salt  was  formerly  used  in  a  manner  altogether  vague. 
Almost  every  substance  which  possessed  sapor,  was  soluble  in  water,  and 
crystallizable,  was  so  called.  The  solid  acids,  and  alkalies,  as  well  as  their 
combinations,  were  therefore  classed  with  the  salts(2).  Under  such  a  no- 
menclature a  salt  might  be  compounded  of  two  simple  substances  only:  thus 
potassa,  which  is  an  oxide  of  potassium,  and  phosphoric  acid,  which  is 
oxygenated  phosphorus,  were  considered  as  members  of  this  family.  Every 
salt,  according  to  the  present  arrangement,  must  be  compounded  of,  at 
least,  two  compound  substances;  every  acid  and  every  salinable  base  being 
itself  a  compound(3). 

Caroline.  Then~every  salt  must  consist  of,  at  least,  four  different  sim- 
ples. 

Emily.  Are  you  not  too  quick  in  your  conclusion,  Caroline?  If  we  com- 
bine the  potassa  and  the  phosphoric  acid,  and  form  phosphate  of  potassa, 
but  three  undecompounded  substances  will  be  contained  in  the  resulting  salt, 
as  oxygen  was  one  of  the  ingredients  in  both  the  combining  articles(4). 

Caroline.  You  have  indeed  fairly  caught  me,  Emily,  and  I,  in  my  turn, 
•will  venture  to  impugn  the  definition  of  the  chemists,  and  say  that  salt 
itself  is  no  salt;  for  are  we  not  told  that  the  very  article  from  which  the 


60.  To  what  uses  has  iodine  been  applied? 

1.  How  may  a  salt  be  defined? 

2.  To  what  substances  was  the  term  formerly  applied? 

3.  What  marked  difference  is  there  between  the  former  and  the  present 
arrangement? 

4.  Does  it  follow  that  a  salt  must  contain  four  simple  substances? 

W 


254  CONVERSATIONS  ON  CHEMISTRY. 

name  is  taken,  the  muriate  of  soda,  is  actually  a  chloride  of  sodium,  and 
consists  therefore  of  two  elementary  substances  only(5)? 

Jlfrs  JS.  Very  well  managed,  Caroline.  If  the  constitution  of  common 
salt  should  be  unequivocally  proved  to  be  such  as  is  supposed  in  the  theory 
to  which  you  have  alluded,  this  very  substance  must  be  banished  from 
the  class  to  which  it  has  given  a  name;  but  neither  its  usefulness  or  its  im- 
portance will  suffer  any  diminution  from  this  cause,  nor  will  the  defini- 
tion of  the  chemist  be  impugned  by  transferring  the  chloride  of  sodium 
from  the  company  in  which  it  has  hitherto  held  a  place  into  another  corps. 
You  may  recollect,  also,  that  it  will  resume  its  former  station  in  nearly  the 
whole  of  its  active  operations,  as  the  water  which  dissolves  it  will  also  con- 
vert it  into  the  muriate  of  soda(6). 

Emily.  To  give  the  name  of  salt  to  a  substance  which  is  altogether 
insipid,  still  seems  to  do  some  violence  to  the  idea  which  the  word  has 
commonly  conveyed  to  the  mind;  as  no  other  test  of  saltness  has  hitherto 
been  known  to  us  but  the  peculiar  taste  possessed  by  a  substance;  and  this 
taste  has  always  been  more  or  less  associated  with  that  of  common  salt. 

J\Trs  JB.  You  now  know,  however,  that  the  class  to  which  any  substance 
belongs  must  depend  upon  its  chemical  constitution,  and  not  upon  a  mere 
accidental  character  which  may  belong  to  the  individual.  The  sapidity  of 
a  salt  depends  upon  its  solubility,  and  consequently  those  which  are  entirely 
insoluble  in  water  must  be  altogether  insipid.  A  solid  substance  put  into 
the  mouth  is  tasteless  if  the  saliva  will  not  dissolve  it,  and  the  intensity  of 
its  taste  will  be  governed  by  the  facility  with  which  it  is  dissolved(7). 

Caroline.  The  facility  or  difficulty  of  solution  must  depend  principally 
upon  the  affinity  between  water  and  the  salt.  Some  salts  1  know  become  moi  st, 
and  even  pass  into  the  liquid  state,  by  mere  exposure  to  the  atmosphere, 
and  these  I  recollect  you  have  called  deliquescent  salts. 

•Mrs  B.  The  cause  you  have  assigned,  together  with  that  of  the  cohe- 
sive attraction  of  the  particles  of  a  salt,  are  the  two  circumstances  which 
govern  its  solubility.  You  will  at  once  see  that  the  more  forcibly  the  parti- 
cles of  a  salt  adhere  together,  the  greater  must  be  the  difficulty  with  which 
water  or  any  other  agent  can  separate  them(8). 

As  respects  the  influence  of  atmospheric  air  upon  them,  salts  are  divided 
into  deliquescent,  efflorescent,  and  permanent^}.  Carbonate  of  potassa, 
muriate  of  lime,  and  many  others  are  deliquescent.  Other  salts,  instead  of 
acquiring  water  from  the  atmosphere,  lose  a  portion  of  that  with  which  they 
were  combined,  and  instead  of  retaining  their  solid  crystalline  form,  fall 
into  powder.  This  process  is  denominated  efflorescence.  Sulphate  of  soda, 
and  sulphate  of  iron,  are  both  efflorescent.  Those  salts  which  undergo  no 
alteration  by  exposure  to  the  air  are  called  permanent(lO}. 

Caroline.  But  if  a  salt  loses  a  portion  of  the  water  which  was  combined 
with  it,  it  loses  one  of  its  constituents  and  must  therefore  be  decomposed. 

Mrs  B.  Perhaps  this  effect  ought  to  be  called  a  disintegration,  rather 
than  a  decomposition  of  the  salt;  as  by  parting  with  water  it  merely  loses  'ts 
crystalline  form,  whilst  its  essential  ingredients,  the  acid  and  the  base,  re- 
main united.  Water  is  absolutely  necessary  to  the  crystallization  of  most 
salts,  combining  with  them  in  definite  proportions.  This  proportion  of 


5.  What  remark  is  made  by  Caroline  respecting  common  salt? 

6.  What  is  the  reply  to  this  observation? 

7.  Why  are  some  salts  sapid,  and  others  tasteless? 

8.  Upon  what  circumstances  does  the  solubility  of  a  salt  depend' 

9.  How  are  salts  classed  as  regards  the  influence  of  air  upon  them' 

10  What  is  intended  by  the  terms  efflorescent,  deliquescent  and  permanent' 


ON  SALTS.  255 

water  is  called  the  -water  of  crystallization,  and  whilst  it  is  retained  as  such, 
it  exists  in  the  solid  form(ll). 

Emily.  I  recollect  you  called  those  bodies  hydrates,  with  which  water  is 
so  intimately  combined  as  to  exist  in  them  as  one  of  their  essential  compo- 
nents(12).  Are  all  crystallized  salts  hydrates? 

Mrs  B.  By  no  means;  for  although  most  crystallized  salts  contain  wa- 
ter as  an  essential  ingredient,  this  is  not  the  case  with  all.  Those  salts 
which  do  not  contain  any  are  called  anhydrous.  Nitre  and  common  salt 
are  both  anhydrotts(l3).  In  some  instances,  the  same  salt  may  exist  in  the 
crystalline  form  in  both  states;  but,  in  this  case,  the  form  of  the  crystal,  and 
some  other  characters  of  the  salt,  will  be  changed.  The  common  borate  of 
soda  is  a  hydrate,  but  there  is  also  an  anhydrous  borate  of  soda;  the  former 
is  slightly  efflorescent,  the  latter  is  permanent.  Common  crystallized  sul- 
phate of  lime  is  also  a  hydrate,  but  there  are  likewise  crystals  of  anhy~ 
drous  sulphate  o/#me(l4). 

Caroline.  I  should  suppose  that  those  salts  which  are  soluble  would,  in 
all  instances,  be  dissolved  in  much  larger  portions  in  hot  than  in  cold 
water,  as  heat  itself  is  a  powerful  solvent. 

Mrs  £.  You  may  well  draw  such  an  inference,  from  the  general  agency 
of  heat,  and  it  is  justified  by  the  greater  number  of  facts  ;  but  still  it  is  not 
a  universal  truth.  The  chlorate  of  soda,  the  phosphate  of  ammonia,  the 
muriate  of  soda,  or  common  salt  of  our  tables,  and  some  others,  are  dissolved 
in  nearly  the  same  proportions  in  cold  as  in  boiling  water(15);  whilst 
there  are  some  salts  that  dissolve  in  quantities  absolutely  unlimited,  when 
the  heat  is  at  the  boiling  point. 

Caroline.  This  seems  equivalent  to  saying  that  they  will  dissolve  in  no 
water  at  all;  as  a  single  drop  of  water  must,  in  this  case,  be  capable  of  dis- 
solving a  thousand  pounds  of  such  a  salt! 

Mrs  Ji.  Such  salts  dissolve  in  their  own  water  of  crystallization,  when 
heated  to  the  boiling  point,  and,  of  course,  the  quantity  dissolvable  is  unlimit- 
ed; as  each  crystal  carries  with  it  the  portion  of  water  necessary  to  its  own 
solution(16). 

Emily.  In  such  salts  the  quantity  of  water  of  crystallization  must,  I  ap- 
prehend, be  very  great. 

Mrs  JB.  The  solution  does  not  depend  entirely  on  the  quantity  of  water 
of  crystallization,  but,  principally,  upon  the  nature  of  the  salt  itself.  More 
than  half  the  weight  of  crystallized  sulphate  of  soda  (Glauber's  salt)  con- 
sists of  water,  its  amount  being  56  per  cent,  yet  it  is  not  soluble  in  its  own 
water  of  crystallization(17). 

Caroline.  I  have  occasionally  seen  Glauber's  salt  thrown  away,  under 
the  impression  that  it  was  spoiled,  because  it  had  become  a  loose  white 
powder,  and  I  now  perceive  that  it  had  merely  parted  with  its  water  of  crys- 
tallization. 

Mrs  B«  Such  a  salt  is  worth  moi-e  per  pound  in  its  effloresced  than  in 
its  crystalline  state,  as  the  weight  lost  is  merely  that  of  water,  and  if  a  quan- 
tity of  boiling  water,  just  sufficient  to  dissolve  the  salt,  were  poured  upon  it 
and  the  solution  allowed  to  cool,  a  crop  of  beautiful  crystals  would  be  ob- 


11.  What  is  water  of   crystallization,   and   what  the  actual    effect  of 
efflorescence  on  a  salt? 

12.  When  are  bodies  denominated  hydrates? 

13.  What  is  remarked  of  salts  in  this  particular? 

14.  What  is  observed  respecting  the  two  states  of  the  same  salt? 

15.  Are  all  salts  dissolved  more  abundantly  by  hot  than  by  cold  water* 

16.  What  salts  dissolve  in  unlimited  quantities  in  hot  water? 

17.  Does  this  depend  on  the  quantity  of  water  of  crystallization? 


256  CONVERSATIONS   ON  CHEMISTRY. 

tained;  as  boiling  water  will  dissolve  nearly  four  times  the  quantity  which 
cold  water  can  retain(18). 

Emily.  I  recollect  that  in  our  conversation  on  the  subject  of  latent  heat, 
(p.  76,)  there  was  an  illustration  of  this  fact,  in  the  crystallizing  of  Glau- 
ber's salt  from  its  solution,  but  the  crystals  then  formed  appeared  to  be  a 
mere  confused  mass. 

Mrs  B.  The  production  of  beautiful  well-formed  crystals  is  a  slow  pro- 
cess, and  it  is  necessary  that  the  solution  should  be  at  perfect  rest,  in  order 
that  the  particles  of  the  salt  may  arrange  themselves  in  the  symmetrical  way 
necessary  to  the  perfection  of  the  process.  In  the  experiment  to  which  you 
allude,  the  crystallization  was  almost  instantaneous(19). 

Caroline.  This  symmetrical  arrangement  called  crystallization  appears 
to  me  to  be  a  very  curious  thing,  and  I  should  be  much  gratified  to  learn 
something  about  the  process  itself;  I  suppose  I  must  not  say  about  its  cause? 

Mrs  B.  I  intend  presently  to  gratify  you  in  this  particular,  but  have  not 
yet  completed  what  I  have  to  say  respecting  some  other  properties  of  salts 
and  their  solutions.  I  am  about  to  show  you  an  experiment  with  two  crys- 
tallized salts,  upon  the  rationale  of  which  you  may  exercise  your  ingenuity; 
it  is  the  reverse  of  the  chemical  miracle  formerly  shown  to  you  (p.  76),  as 
it  consists  in  the  conversion  of  two  solids  into  a  fluid,  by  mixing  them  to- 
gether. I  take  equal  portions  of  crystallized  sulphate  of  soda,  and  muriate 
of  ammonia;  both,  of  course,  in  a  solid  and  dry  state.  I  now  rub  them  in- 
timately together  in  a  mortar,  and  you  see  the  result. 

Emily.  That  is  extremely  curious,  they  are  actually  in  a  state  of  solu- 
tion, as  much  so  as  though  you  had  poured  water  upon  them(20). 

Mrs  B.  I  think  that  by  the  aid  of  our  present  conversation,  you  will  be 
able  to  account  for  this  change.  I  will  observe,  however,  that  a  double  de- 
composition has  taken  place,  and  that,  instead  of  sulphate  of  soda,  and  muriate 
of  ammonia,  we  have  produced  a  muriate  of  soda  and  a  sulphate  of  ammo- 
nia, these  two  salts  being  now  in  a  state  of  mixture. 

Caroline.  In  the  decomposition  of  the  original  salts,  their  water  of 
crystallization  must  have  been  set  at  liberty,  and  its  quantity  must  have  been 
sufficient  to  dissolve  the  new  salts  which  are  formed(21). 

Mrs  B.  You  have  given  the  rationale  correctly,  as  1  was  convinced  you 
would.  These  double  decompositions,  which  result  from  the  mixture  of 
two  different  salts,  have  given  rise  to  the  name  of  incompatible  salts,  tables  of 
which  you  will  find  in  some  of  the  treatises  on  chemistry.  By  incompatible 
salts  are  meant  those  which  cannot  exist  together  in  solution  without  mu- 
tual decomposition.  Such  were  the  salts  which  we  just  now  mixed  to- 
gether^). 

Emily.  The  muriate  of  soda  which  is  contained  in  the  water  of  the 
ocean,  is  mixed  with  a  great  number  of  other  salts.  Nitre  likewise,  and  in 
fact  most  of  the  salts  in  their  crude  state  are  contaminated  by  the  presence 
of  others;  upon  what  principle  is  their  separation  effected? 

Mrs  B.  To  effect  this  separation  the  chemist  takes  advantage  of  the 
difference  in  the  solubility  of  the  respective  salts.  When  these  mixed  salts 
have  been  dissolved,  the  water  is  evaporated  to  a  certain  extent,  and  hy  mere- 
ly allowing  the  solution  to  remain  at  rest  for  some  days,  that  salt  which  is 
least  soluble  is  deposited  in  the  crystalline  form.  From  these  crystals  the 
mother -water,  as  the  solution  is  now  called,  may  be  poured  off.  This  may  be 
still  further  evaporated,  and  made  to  deposite  a  second  crop  of  salt,  of  a  kind 


18.  What  is  remarked  respecting  an  effloresced  salt? 

19.  Upon  what  does  regular  crystallization  depend? 

20.  What  two  solid  salts  become  fluid  by  mixture? 

21.  In  what  way  is  this  solution  explained? 

22.  When  are  salts  said  to  be  incompatible? 


ON  SALTS.  257 

more  soluble  than  the  former,  and  which  was  therefore  retained  by  the  water, 
until  its  quantity  was  reduced  by  the  second  evaporation.  By  repeated  solu- 
tions and  crystallizations,  in  this  way,  the  respective  salts  may  be  obtained  in 
a  separate  state,  which,  but  for  the  difference  in  their  solubility,  must  forever 
have  remained  mixed  with  each  other.  The  refining'  of  nitre  and  other 
salts  is  thus  effected(23). 

Caroline.  I  am  aware  that  it  would  be  impossible  to  separate  the  crys- 
tals of  different  salts  which  were  grouped  together;  but  if  there  are  two  or 
three  different  salts  in  the  same  solution,  and  the  whole  of  the  water  was  to 
be  evaporated,  would  not  the  particles  of  each  salt  unite  to  those  of  its  own 
nature,  and  form  distinct  crystals? 

J\Irs  B.  They  would,  and  their  different  forms  may  frequently  be  seen 
in  the  mass  of  crystals.  This  fact  is  very  satisfactorily  exhibited  where  one 
of  the  salts  is  coloured,  as  I  am  prepared  to  show  you.  I  have  dissolved  in 
the  same  hot  water,  portions  of  nitre,  which  is  colourless,  and  of  sulphate 
of  copper,  which  is  blue;  this  solution  I  have  poured  into  a  plate,  and  suf- 
fered it  to  cool.  The  salts,  you  see,  have  crystallized  separately(24). 

Emily.  How  beautiful  they  appear,  and  how  distinct!  They  look  like 
white  and  blue  gems  grouped  together,  and  are  as  completely  distinguished 
by  their  respective  forms  as  by  their  colours. 

Caroline.  Nothing  certainly  could  exemplify  more  strikingly,  or  more 
satisfactorily,  the  controlling  attraction  which  the  similar  particles  exert  to- 
wards each  other.  Aided  by  the  difference  in  colour,  we  might  now  sepa- 
rate the  salts  from  each  other,  almost  perfectly(25). 

Jlfrs  JB.  You  are  aware  that  water  at  a  given  temperature  will  dissolve 
only  a  definite  portion  of  a  salt,  and  that  it  is  then  saturated.  It  is  a  fact, 
however,  that  water  saturated  with  one  salt,  may  still  dissolve  a  quantity  of 
a  second,  and  that  the  dissolving  of  this  last  will  enable  it  to  combine  with 
more  of  the  former.  Thus,  for  example,  water  saturated  with  common  salt, 
will  afterwards  dissolve  nitre,  and,  when  it  has  done  so,  will  take  up  an  ad- 
ditional portion  of  the  muriate  of  soda(26). 

Emily.  That  is  indeed  curious;  but  I  suppose  it  can  be  satisfactorily  ac- 
counted for. 

Mrs  B.  It  appears  to  result  from  an  attraction  existing  between  the  two 
salts,  which,  added  to  the  attraction  of  the  water,  increases  the  power  of 
combination.  When  the  solution  of  common  salt  has,  from  this  cause,  dis- 
solved a  portion  of  the  nitre,  this,  in  its  turn,  lends  its  attractive  influence  to 
the  water,  and  enables  it  to  increase  its  charge  of  the  muriate  of  soda(27). 

Caroline.  But  if  these  salts  can  be  again  separated  by  crystallization,  the 
attraction  which  promoted  their  solution  must  still  have  been  insufficient 
for  their  decomposition.  I  can  very  well  conceive  of  such  an  attraction, 
and  think  that  its  existence  must  aid  in  accounting  for  many  phenomena(28). 

Jlfrs  B.  The  existence  of  such  an  attraction  is  frequently  made  manifest. 
Even  those  salts  which  are  incompatible  may,  by  a  very  simple  precaution,  be 
mixed  together  without  decomposing  each  other;  all  that  is  necessary  being 
to  dilute  them  with  a  large  quantity  of  water.  They  will  then  remain  together 
unchanged,  yet  the  attraction  of  their  elements  must  still  exist,  although  it  is 
counteracted  by  the  water  employed  for  their  solution,  in  consequence,  pro- 
bably, of  its  removing  their  respective  particles  very  far  from  each  other(29) 


23.  How  may  salts  in  solution  be  separated  from  each  other? 

24.  Describe  the  experiment  of  nitre  and  sulphate  of  copper. 

25.  What  fact  does  this  experiment  serve  to  illustrate  ? 
i?6.  What  is  said  of  a  solution  saturated  with  one  salt? 

27.  What  explanation  is  given  of  this  phenomenon? 

28.  What  is  remarked  respecting  an  attraction  of  this  kind? 

29.  WThen  may  incompatible  salts  exist  together  in  solution? 

W2 


258  CONVERSATIONS  ON  CHEMISTRY. 

Emily.  Are  there  no  instances  in  which  different  salts,  when  mixed  to- 
gether in  solution,  combine  and  form  one  common  compound  salt,  insepa- 
rable by  crystallization  ? 

Mrs  JS.  There  are  some  such;  and  the  resulting  combinations  have  been 
usually  called  triple  salts;  but  perhaps  the  term  double  salts  would  give  a 
more  correct  idea  of  their  composition.  Such  salts  usually  consist  of  one 
acid  united  to  two  different  bases(30).  Common  alum,  formerly  noticed, 
(p.  179),  is  one  of  these.  It  is  usually  called  the  sulphate  of  alumine,  but 
more  properly  sulphate  of  alumine  and  potash,  as  it  consists  of  sulphuric 
acid  united  to  both  alumine  and  potassa.  Rochelle  salt,  also,  has  a 
double  base,  consisting  of  potash  and  soda,  which  are  united  to  a  vegetable 
acid  called  tartaric  acid.  This  salt,  therefore,  is  properly  a  tartrate  of 
potash  and  soda.  These  may  suffice  as  examples  of  the  double  salts,  which 
do  not  form  a  very  extensive  class(31). 

We  have  now  touched  upon  the  most  important  points  respecting  the 
salts  as  a  class.  The  greater  number  of  them  are  capable  of  crystallisation, 
but  this  is  a  property  which  they  possess  in  common  with  most  of  the  bodies 
in  nature.  We  are  more  familiar,  however,  with  saline  than  with  other  crys- 
tals. But  tell  me,  Caroline,  what  do  you  understand  by  a  crystal? 

Caroline.  By  a  crystal,  I  understand  a  body  which,  in  becoming  solid 
from  its  solution,  assumes  a  certain  regular  symmetrical  form,  with  flat  sides 
and  regular  angles,  appearing  as  though  it  had  been  formed  by  art(32). 

Mrs  JS.  Your  definition  is  very  good,  and,  I  may  add,  unobjectionable, 
provided  you  employ  the  term  solution  in  its  broadest  sense.  Many  articles 
crystallize  which  are  dissolved  by  heat  alone.  Thus  several  of  the  metals 
assume  a  crystalline  form,  on  being  allowed  to  cool  slowly  after  having  been 
fused.  Sulphur  also,  and  many  other  substances  which  undergo  fusion, 
exhibit  the  same  tendency.  The  particles  of  the  greater  number  of  those 
solids  which  are  capable  of  sublimation,  likewise  arrange  themselves  in 
symmetrical  forms,  as  they  consolidate  by  cooling(33). 

Emily.  I  have  often  admired  the  crystals  in  cabinets  of  minerals,  where 
many  of  the  native  metals,  and  the  solid  insoluble  earths,  are  seen  moulded 
by  nature  into  regular  and  beautiful  shapes.  It  seems  difficult  to  conceive 
how  insoluble  substances  should  assume  these  forms. 

Mrs  B.  Nature,  for  the  perfection  of  her  operations,  has  a  variety  of 
means,  and  an  extent  of  time,  at  her  disposal,  which  set  at  nought  the  labour 
of  man,  during  his  brief  existence.  A  substance  which  would  require  for 
its  solution  many  thousand  times  its  weight  of  water,  may  by  us  be  well 
deemed  insoluble;  as  under  our  control  it  might  not,  during  the  continu- 
ance of  our  lives,  form  a  visible  crystal.  Art,  therefore,  must  completely 
fail  when  she  would  essay  to  imitate  nature  in  such  a  work(34). 

The  subject  of  the  formation  of  crystals,  by  the  aggregation  of  their  con- 
stituent particles,  is  one  which  is  well  worthy  of  your  examination.  It  is 
sufficiently  extensive,  however,  to  deserve  the  devotion  of  more  time  to  it 
than  the  remainder  of  the  present  evening  would  admit.  The  salts^have 
detained  us  longer  than  I  had  anticipated.  I  therefore  postpone  the  subject 
of  crystallography  until  to-morrow,  although  I  had  anticipated,  and  prepar- 
ed for,  its  introduction  to-day. 


30.  What  are  double  salts,  and  how  may  they  be  formed? 

31.  What  examples  are  given  of  the  formation  of  double  salts? 

32.  What  is  a  crystal  defined  to  be? 

33.  Under  what  circumstances  do  some  metals  and  other  solids  crys- 
tallize? 

34.  Why  cannot  we  imitate  some  natural  crystals? 


259 


CONVERSATION  XXVI. 

ON  CRYSTALLOGRAPHY. 

Advantages  derived  from  Crystallography.  Bodies  in  general  suscepti- 
ble of  Crystallization.  Different  Forms  assumed  by  different  Bodies.  Pri- 
mary and  Secondary  Forms.  Integrant  Particles,  or  Molecules.  Deriva- 
tion of  the  Rhombic  Dodecahedron  from  the  Cube.  Conversion  of  the 
Octahedron  into  a  Cube,  and  of  the  Cube  into  an  Octahedron  by  mechanical 
Division.  Dr  Wollaston's  Theory  of  the  Formation  of  Crystals  from  spheri- 
cal Particles.  Exemplified  in  the  Piling  of  Balls.  Illustration  of  the  Pro- 
duction of  various  Crystalline  Forms  in  this  -way. 

Mrs  B.  The  crystalline  form  is  assumed  by  so  large  a  number  of  sub- 
stances, and  appears  under  aspects  so  different  in  different  bodies,  as  to 
have  supplied  us  with  a  character  by  which  we  are  frequently  enabled  to 
distinguish  them  from  each  other.  The  composition  of  a  body  is  thus  fre- 
quently ascertained  without  therlabour  of  analysis(l).  Most,  and  probably 
the  whole  of  the  simple  solids  are  capable  of  crystallization,  and  there  is 
not  any  body  which,  either  alone  or  in  combination,  does  not  admit  of  that 
arrangement  of  its  particles  which  presents  it  to  us  with  symmetrical  and 
well  denned  faces  and  angles(2). 

The  science,  the  object  of  which  is  to  inquire  into  the  laws  which  obtain  in 
the  formation  of  crystals,  is  called  CRYSTALLOGRAPHY.  It  is  one  of  conside- 
rable intricacy,  and  which  has  occupied  the  attention  of  many  of  the  ablest 
philosophers.  Without  attempting  to  follow  them  in  their  abstruse  specu- 
lations, we  may  advantageously  survey  the  outlines  of  their  discoveries. 

Emily.  Do  not  the  same  substances  always  assume  the  same  form  when 
they  crystallize? 

Mrs  B.  Every  solid  that  is  susceptible  of  crystallization,  has  a  ten- 
dency to  assume  a  particular  shape.  Thus,  common  salt,  when  most  per- 
fectly crystallized,  forms  regular  cubes;  nitre  has  the  shape  of  a  six-sided 
prism;  alum  that  of  an  octahedron;  whilst  carbonate  of  lime  produces  a  re- 
gular rhomboid.  The  same  substance  however  is  frequently  found  under  a 
great  variety  of  forms:  thus  we  have  carbonate  of  lime  in  six-sided  prisms, 
in  three  or  six-sided  pyramids,  and  in  a  great  number  of  other  shapes(3). 

Caroline.  That  fact  destroys  all  my  fine  theory,  for  I  had  supposed  that  the 
shape  of  the  crystal  depended  upon  that  of  the  atoms  of  which  it  is  compo- 
sed 5  as  for  example,  by  putting  a  great  number  of  small  cubes  together,  we 
might  easily  make  a  cube  of  any  imaginable  size. 

Mrs  B.  It  may  be  some  satisfaction  to  you  to  be  told  that,  whether  your 
theory  be  true  or  false,  the  fact  which  I  have  mentioned  does  not,  in  the 
slightest  degree,  militate  against  it;  as  all  the  forms  of  carbonate  of  lime  to 
which  I  have  alluded,  may  be  produced  by  the  combination  of  rhomboidal 
crystals.  It  is  a  fact,  also,  that  we  can  take  one  of  these  more  complex  crys- 
tals, a  six-sided  prism  for  instance,  and  divide  it,  mechanically,  into  per- 
fect rhomboids(4). 

Caroline.  I  am  indeed  pleased  that  my  theory  has  escaped  so  far?  it 
has  already  outlived  several  of  its  predecessors. 

Mrs  B.     From  the  cause  stated,  the  forms  under  which  crystals  appear 


1.  What  advantage  does  a  knowledge  of  crystalline  forms  afford? 

2.  Do  bodies  in  general  undergo  crystallization? 

3.  What  is  said  of  the  crystalline  forms  of  the  same  body? 

4.  What  is  remarked  respecting  crystals  of  carbonate  of  lime? 


260 


CONVERSATIONS  ON  CHEMISTRY. 


have  been  divided  into  primary,  and  secondary.  By  the  primary  form  is 
intended  that  into  which  a  crystal  may  be  reduced  by  mechanical  division, 
or  to  which  it  may  be  proved,  by  calculation,  that  it  is  reducible.  By  se- 
condary forms  are  intended  all  those  which  result  from  the  various  combi- 
nations of  the  primary  crystals.  The  first  are  but  few  in  number;  the 
second  are  very  numerous,  in  consequence  of  the  many  different  ways  in 
•which  the  primitive  crystals  may  be  piled  upon  each  other(5). 

Emily.  These  wooden  models  are  intended,  I  suppose,  to  show  the  va- 
rious primitive  forms. 

Mrs  B.  That  is  their  principal,  hut  not  their  only, design,  as  you  will 
presently  learn.  There  is  some  difference  of  opinion  respecting  the  actual 
number  of  primitive  forms,  but,  most  generally,  they  are  confined  to  six,  and 
this  arrangement  we  shall  follow(6). 

The  FIRST  is  the  parallelopipedon,  or  a  figure  terminated  by  six  faces,  the 
opposite  ones  being  all  parallel  to  each  other.  This  includes  three  princi- 
pal varieties;  the  cube,  the  four-si ded prism,  and  the  rhomboid  (Fig.  1,  2, 
and  3),  which  are  those  before  you. 


Cube. 


PABALLELOPIPEDOXS . 

Four-sided  Prism. 


Rhomboid. 


Fig.   1. 


Fig.  3. 


Fig.  2. 


Caroline.  The  similarity  between  the  two  first  of  these  is  very  apparent, 
as  two  cubes  joined  together  would  produce  the  four  sided  prism(7). 

Mrs  B.  The  SECOND  of  the  primitive  forms  is  the  tetrahedron;  which 
is  a  figure,  as  you  know,  with  four  triangular  sides,  all  the  triangles  being 
equilateral.  (Fig.  4,  5,  and  6.) 


Seen  from  the  top. 


TETRAHEDRON. 

Side  view. 


Fig.  4. 


Outline  showing  the 
four  sides. 


Fig.  5. 


Fig.  6. 


5.  What  is  the  difference  between  primary  and  secondary  forms? 

6.  What  number  of  forms  are  generally  considered  as  primary  ? 

7.  What  is  the  first  form,  and  what  are  its  varieties? 


ON  CRYSTALLOGRAPHY. 


261 


The  THIRD  is  the  octahedron,  which,  as  its  name  indicates,  is  a"  figure  with 
eight  sides,  and  may  be  considered  as  consisting  of  two  four-sided  pyramids 
joined  together  at  their  bases.  (Fig.  7  and  8). 

The  FOURTH,  the  hexangular,  or  six-sided  prism,  (Fig  9  and  10);  of 
which  nitre  and  rock  crystal  may  furnish  examples(8). 


Octahedron. 


The  same  in  outline. 


Fig.   7. 


Fig.  8. 


Hexangular 
prism. 


Fig.   9. 


The  same   in 
outline. 


Fig.   10. 


The  FIFTH,  the  rhombic  dodecahedron,  (Fig.  11  and  12);  a  figure  with 
twelve  sides,   each  of  which  is  a  rhomb. 

The  SIXTH,   the  dodecahedron  -with  triangular  faces,  (Fig.  13  and  14); 
•which  consists  of  two  six-sided  pyramids,  united  at  their  bases(9). 

Rhombic  The  same  in         Dodecahedron    The  same  in 

Dodecahedron.  outline.  -with   triangu-        outline, 

lar  faces. 


Fig.   11 


Fig.   13. 


Fig.   14. 


Caroline.  It  seems  to  me  as  though  some  of  these  six  forms  which  you 
call  primitive  may  themselves  be  composed,  or  built  up,  as  it  were,  of 
others  still  more  simple;  yet  the  name  primitive  would  seem  to  indicate 
that  these  were  actually  the  most  simple  forms  into  which  they  could  be  re- 
duced, either  actually,  or  mathematically (10).  • 

JYTrs  B.  Such  however  is  not  the  idea  which  the  name  is  intended  to 
convey.  By  the  primitive  form  is  meant  that  into  which  the  crystal  may, 
in  general,  be  reduced  by  mechanical  division, in  a  way  to  be  presently  ex- 
plained. But  it  is  capable  of  mathematical  proof,  that  all  these  six  primi- 
tive forms  may  be  composed  of  three  simple  solids;  the  tetahedron,  the 
simplest  of  pyramids;  the  triangular  prism,  the  simplest  of  prisms;  and  the 
parallelopipedon,  including  the  cube  and  rhomboid,  the  simplest  of  solids 
with  parallel  faces.  (Fig.  15,  16, 


8.  Give  a  description  of  the  second  third  and  fourth  species. 

9.  Describe  the  two  last  of  these  primitive  forms. 

10.  What  observation  is  made  concerning  these  primitive  forms? 

11.  Into  what  simple  solids  may  all  these  be  reduced? 


262 


CONVERSATIONS  ON  CHEMISTRY. 


Tetrahedron.          Triangular  Prism. 


Paralklopi-   Hexangular  Prism, 
pedon. 


•\ 


Fig.  15. 


Fig.  16. 


Fig.   17. 


VV 

Fig.   18. 


By  drawing  lines  from  angle  to  angle,  across  the  centre  of  this  hexangular 
prism,  (fig.  18),  it  will  be  divided  into  equilateral  triangles.  It  is  plain 
therefore  that  this  six-sided  crystal  might  itself  be  composed  of  triangular 
prisms.  In  like  manner  a  parallelopipedon  would  be  produced  by  joining 
together,  face  to  face,  two  only  of  the  triangular  prisms(12). 

Emily.  This  is  very  satisfactery,  and  seems  to  accord  with  the  gene- 
ral simplicity  of  the  means  by  which  nature  operates.  By  what  term  are 
these  simple  forms  designated,  so  as  to  distinguish  them  from  the  primary 
forms? 

Mrs  B.  These  have  been  called  integrant  particles,  or  molecules. 
When  a  single  atom  of  an  acid  unites  to  an  atom  of  any  salifiable  base,  there 
will  be  produced  by  their  combination  an  integrant,  or  individual  atom  of  a 
salt.  Thus  an  atom  of  carbonic  acid  may  unite  to  an  atom  of  lime,  and  the 
necessary  result  of  this  union  will  be  the  formation  of  an  integrant  particle, 
or  single  atom  of  carbonate  of  lime.  Now  it  is  plain  that  this  integrant  par- 
ticle must  possess  some  determinate  form:  it  may  itself  be  a  rhomboid,  or 
this  figure  may  be  produced  by  the  junction  of  two  of  these  integrant  parti- 
cles, thus  giving  rise  to  a  primary  crystal  of  carbonate  of  lime.  By  the  ac- 
cumulation of  a  large  number  of  these,  attaching  themselves  regularly  to 
each  other  by  the  attraction  of  aggregation,  a  visible  rhomboidal  crystal 
must  at  length  be  produced.  As  a  crystal  so  composed  is,  from  its  nature, 
incapable  of  being  reduced  into  a  more  simple  figure  than  the  rhomboid,  we 
should  call  it  the  primary  form,  which,  in  the  case  we  have  supposed,  would 
be  the  same  as  that  of  the  integrant  molecule(13). 

Caroline.  The  atomic  theory  has  rendered  us  tolerably  familiar  with 
the  idea  of  particles,  which  greatly  aids  us  in  this  attempt  to  trace  their 
mechanical  arrangement ;  and  this  subject,  which  I  thought  would  be 
rather  uninteresting,  is  one  that  has  already  afforded  me  much  satisfac- 
tion. I  shall  frequently  amuse  myself  with  tracing  the  forms  which  these 
integrant  particles  may  produce  by  their  combination.  I  fear  however  that 
I  shall  not  be  able  from  either  of  them  to  construct  a  rhombic  dodecahedron. 

Mrs  B.  Yet  this  may  be  derived  from  the  cube,  the  most  familiar  of 
these  integrant  solids.  The  mode  in  which  this  may  be  done,  will  be 
clearly  illustrated  by  means  of  this  model.  That  integrant  cubes  may  be 
built  upon  each  other  so  as  to  form  figures  similar  to  themselves,  and  of 
any  dimensions,  you  have  already  remarked.  Now  suppose  these  minute 
cubes  to  have  produced  a  large  cubical  crystal:  an  examination  of  the  model 
will  show  you  how,  upon  this  as  a  nucleus,  other  minute  cubes  may  be  so 
piled  as  to  furnish  a  solid  with  twelve  faces,  each  of  which  shall  be  a 
rhomboid(l4). 


13.   How  might  an  hexangular  prism  be  reduced  into  triangular  prisms? 

13.  What  is  said  respecting  integrant  particles,  or  molecules? 

14.  From  what  integrant  particle    rnay    the  rhombic   dodecahedron  be 
derived? 


ON   CRYSTALLIZATION. 


263 


I  have  a  number  of  other  models  which  exhibit,  with  equal  clearness,  the 
production  of  man}'  other  secondary  crystals;  hut  as  my  design  is  merely  to- 
enable  you  to  pursue  the  inquiry  hereafter,  I  should  rather  embarrass  than 
aid  you  by  producing  any  other  than  the  rhombic  dodecahedron. 

Formation  of  the  Rhombic  Dodecahedron  from  Integrant  Cubes. 


Fig.  19. 

Emily.  Your  model  renders  the  mode' of  forming  such  a  crystal  so  clear 
as  scarcely  to  require  any  explanation.  After  the  cubical  nucleus  is  formed, 
•with  its  six  regular  faces,  you  suppose  other  integrant  cubes  to  be  piled 
upon  each  of  them,  but  receding  from  the  edge,  by  standing  upon  the  se- 
cond row  of  particles,  and  so  continuing,  by  invisible  steps,  until  a  pyra- 
mid is  formed.  The  model  renders  it  quite  evident  that  when  this  has  been 
done  upon  two  contiguous  sides,  a  perfect  rhombic  face  will  be  produced; 
and  I  plainly  see  that  when  all  the  si<fes  have  been  so  treated,  a  twelve- 
sided  solid  with  rhombic  faces  will  be  the  result  of  the  arrangement(15). 

Mrs  B.  Three  of  the  faces  on  the  cube  are  left,  to  show  the  original 
nucleus;  and  it  will  be  readily  conceived  by  you,  that  instead  of  receding 
from  the  edges  by  a  single  row  of  particles,  the  new  layers  may  be  placed 
two,  three,  or  more  rows  back,  and  thus  a  great  variety  of  other  forms  may 
be  obtained,  which,  on  a  cursory  examination,  may  not  appear  to  be  related 
to  the  one  which  we  have  examined,  although  derived  from  the  same 
root(16).  It  is  in  consequence  of  such  arrangements,  that  we  find  in  nature 
that  variety  of  crystals  of  the  same  substance  which  constitutes  the  se- 
condary  forms.  These  four  models  will  still  further  exemplify  the  pro- 
duction of  secondary  forms.  The  first  (fig.  20)  exhibits  a  cube,  the  eight 
angular  points  of  which  are  wanting,  and  are  replaced  by  triangular  faces* 
The  second  (fig.  21)  shows  the  effect  produced,  when  instead  of  the  angular 
points,  the  edges  are  wanting.  The  third  and  fourth  (fig.  22  and  23)  ex- 
emplify the  same  facts  in  relation  to  the  octahedron(17). 


15.  Describe  the  mode  of  producing  it  from  cubes. 

16.  By  what  arrangement  may  they  produce  other  crystals? 

17.  How  is  this  exemplified  by  fig.  20,  21,  22  and  23? 


264 


CONVERSATIONS  ON  CHEMISTRY. 


Caroline.  If  I  am  not  mistaken,  the  cube  (fig.  20)  would  be  converted 
into  an  octahedron,  and  the  octahedron  (fig.  22)  into  a  cube,  by  continuing 
to  slice  off  the  angles,  which  are  wanting  in  the  models. 


Fig.   20. 


Fig.  21. 


Fig.   22. 


Fig.   23. 


Mrs  _Z?.  You  are  not  mistaken,  and  the  correctness  of  your  remark  must 
fully  convince  you  how  completely  the  primary  and  secondary  forms  may 
differ  from  each  other,  whilst  they  are,  in  fact,  mathematically  allied(18). 
A  cubic  crystal  of  fluate  of  lime  may  be  readily  reduced  to  an  octahedron, 
by  cutting  off  its  angles,  in  the  manner  represented  (fig.  20);  and  most  other 
secondary  crystals,  may,  in  like  manner,  be  made  to  exhibit  their  primitive 
forms.  An  attempt  to  cut  them  in  any  other  direction  would  fail,  and  if 
persisted  in  would  produce  a  common  fracture,  instead  of  a  smooth  regular 
surface(19). 

Caroline.  The  different  crystalline  forms  which  bodies  assume,  seem, 
certainly,  to  justify  the  opinion  that  the  integrant  particles,  or  constituent 
atoms  of  matter,  are  various  in  their  shape,  and  thus  give  rise  to  a  variety 
of  symmetrical  figures  in  crystallized  bodies;  but  for  this  I  should  have 
retained  the  idea,  which,  I  believe,  very  generally  prevails,  that  they  are 
all  spherical. 

Emily.  And  perhaps  they  are  so;  for,  certainly,  symmetrical  figures  may 
be  produced  by  spheres,  as  well  as  by  triangular  prisms  and  rhomboids. 
Do  you  not  recollect  how  we  admired  the  different  forms  in  which  the  balls 
were  piled  at  the  arsenal?  Why  may  not  the  various  forms  of  crystals  be, 
in  like  manner,  produced  by  the  accumulation  of  round  particles(20)? 

Mrs  JS.  The  opinion  that  the  constituent  particles  of  matter  are  either 
perfect  spheres  or  spheroids,  has  been  sustained  by  one  of  the  first  philo- 
sophers of  the  age,  Dr  Wollaston,  whose  name  has  been  before  men- 
tioned to  you.  It  is  a  fact  that  some  of  the  crystalline  forms  are  but  im- 
perfectly accounted  for,  upon  the  supposition  of  their  being  derived  from 
the  three  integrant  particles;  there  being  secondary  forms  which  they  can- 
not produce  without  leaving  spaces  between  them;  that  is,  they  could  not 
every  where  touch  each  other  by  their  flat  sides(21). 

Caroline.  I  am  not  a  little  pleased  to  find  that  I  may  return  to  the 
spheres  in  such  good  company.  The  balls  at  the  arsenal,  as  Emily  ob- 
serves, seem  to  lend  a  powerful  support  to  the  theory  of  round  particles. 

Mrs  _B.  I  have  some  models  of  crystals  supposed  to  be  formed  in  this 
way,  and  which  you  have  not  yet  seen.  They  are  made  simply  of  small 
leaden  shot,  cemented  together  by  gum-water.  The  first  (fig.  24)  is  the 
simplest  mode  of  combining  such  balls,  a  combination  in  which  they  form 
an  equilateral  triangle. 


18.  To  what' form  could  fig.  20  and  22  be  thus  reduced? 

19.  What  is  remarked  respecting  a  cubical  crystal  of  fluate  of  lime,  and 
other  secondary  crystals? 

20.  What    observations   are   made     respecting  the   form  of    integrsmt 
particles? 

21.  What  theory  did  Dr  Wollaston  advance  respecting  them? 


ON  CRYSTALLIZATION. 


265 


Equilateral  Tri- 
angle. Tetrahedron. 


Triangular 
Prism. 


Parallelepiped. 


Fig.   25. 


Fig.  26. 


Fig.   27. 


If  between  these,  others  are  piled,  the  form  of  a  triangular  pyramid,  or 
tetrahedron  (fig.  25)  will  be  produced.  A  number  of  the  equilateral  trian- 
gles (fig.  24)  placed  directly  upon  each  other,  supplies  us  with  the  triangu- 
lar prism  (fig.  26).  The  parallelepiped  (fig.  27)  is  readily  produced,  as  you 
see,  by  the  arrangement  shown  in  this  model(22). 

Emily.  We  have  now  all  the  integrant  molecules,  and  from  these,  of 
course,  all  the  primary  and  secondary  forms  may  proceed,  just  2*8  in  th$ 
former  instance. 

Jlfrs  B.  In  order  to  remove  the  difficulty  in  making  up  certain  existing 
forms  by  perfect  spheres,  Wollaston  supposed,  as  I  have  already  intimated, 
that  the  constituent  atoms  of  some  species  of  matter  are  spheroidal,  that 
is,  not  perfect  spheres(23).  This,  like  every  .thing  relating  to  ultimate 
particles,  is  evidently  hypothetical;  and  if  hypothesis  is  ever  to  be  admit- 
ted, it  must  be  in  such  a  case,  where,  from  our  limited  power  of  percep- 
tion, it  is  impossible  that  we  should  arrive  at  absolute  certainty (24). 

Caroline.  Since  then,  on  such  a  subject,  you  do  not  interdict  hypotheses 
altogether,  I  may  be  still  allowed  to  suppose  that  the  constituent  atoms  of 
matter  may  be  spheres;  that  these  may  combine  together  so  as  to  form  the 
integrant  molecules  ;  and  that  the  integrant  molecules  may  then  arrange 
themselves  exactly  as  was  imagined  in  the  first  instance. 

Mrs  JB.  Such  a  conjecture  is  not  only  admissible,  but  has  as  much,  at 
least,  of  probability  on  its  side,  as  any  other  theoretical  opinion,  upon  this 
subject,  which  has  been  proposed. 

Although  you  can  now  deduce  all  the  different  crystals  from  the  accumu- 
lation of  spheres,  yet  as  I  have  three  other  models  prepared,  which  exhibit 
three  of  the  primary  forms,  you  will  undoubtedly  like  to  examine  them. 
Here,  (fig.  28)  we  have  the  perfect  cube;  the  next  (fig.  29)  has  the  shot  so 


Fig.   28. 


Fig.   29. 


Fig.  30. 


piled  on  each  side  of  a  square  as  to  complete  the  octahedron;  whilst  the 
third  (fig.  30)  gives  you  the  hexangular  or  six-sided  prism(25). 

Emily.     I  am,  of  course,  aware  that  the  integrant  molecules  of  a  crystal 


22.  What  are  fig.  24,  25,  26  and  27  intended  to  illustrate? 

23.  What  is  required  to  remove  some  difficulties  in  this  theory? 

24.  What  renders  hypothesis  admissible  in  such  a  caae? 

25.  What  is  represented  by  fig.  28,  29  and  30? 

A 


266  CONVERSATIONS  ON  CHEMISTRY. 

are  too  minute  to  become  objects  of  vision,  and  that  "whether  particles  be 
round  or  square,  they  may  retire  from  each  other,  in  steps,  as  it  were,  and 
yet  present  surfaces  apparently  unbroken(26);  but  is  not  such  a  structure 
sometimes  rendered  visible  by  the  aggregation  of  larger  particles  than 
usually  go  to  the  formation  of  a  crystal? 

Mrs  JB.  Such  is  actually  the  fact:  these  minute  steps  are  not  unfre- 
quently  exhibited  on  certain  crystals,  and  I  have  some  among  my  minerals 
in  which  they  are  quite  observable(27). 

We  have  now  concluded  our  examination  of  those  substances  which  be- 
long to  the  mineral  kingdom.  In  our  next  conversation  we  shall  commence 
with  those  more  complex  beings  which  belong  to  the  animal  and  vegetable 
creation,  the  consideration  of  which  will  complete  our  chemical  course. 

Caroline.  I  had  hoped,  my  dear  Mrs  B.  that  in  some  part  of  our  con- 
versations you  would  have  favoured  us  with  an  explanation  of  the  nature  of 
the  steam  engine.  But  I  suppose  that  the  consideration  of  this  subject  be- 
longs rather  to  natural  philosophy  than  to  chemistry. 

Mrs  B.  It  is  difficult  to  say  to  which  department  of  science  we  are  most 
indebted  for  the  high  degree  of  perfection  to  which  this  machine  has  been 
brought  within  the  last  age.  It  was  not  introduced  to  you  in  our  conver- 
sations on  natural  philosophy,  because  without  an  intimate  knowledge  of  the 
nature  of  steam,  and  particularly  of  the  doctrine  of  latent  heat,  the  operation 
of  the  steam  engine  can  be  but  very  imperfectly  understood.  But  if  it  is 
your  wish,  we  will  devote  our  next  meeting  to  an  examination  of  the  struc- 
ture and  action  of  this  wonderful  instrument. 

Emily.  We  shall  indeed  be  most  gratified  to  do  so,  and  shall  welcome 
the  hour  which  is  to  afford  us  some  insight  into  a  subject  so  interesting,  and 
respecting  which  we  are  now  completely  in  the  dark. 


CONVERSATION  XXVII. 

ON  THE  STEAM  ENGINE. 

"     ' 

Steam  used  to  produce  Motion  6y  Hero  of  Greece.  Mr  Watt,  the  greatest 
improver  of  the  Steam  Engine.  Admission  of  Steam  alternately  above  and 
below  a  Piston  in  a  Cylinder.  The  Steam  Pipe,  Eduction  Pipe,  Condenser, 
and  Jiir  Pump.  Lo-w  Pressure  Engine.  Mode  of  setting  an  Engine  to 
toork.  Rotary  produced  by  a  Vibratory  Motion.  Safety  Valve.  At- 
mospheric Engine.  Waifs  Engine.  Fly  Wheel.  Parallel  Motion.  JVa- 
ture  of  the  High  Pressure  Engine. 

"•'   v  ^ 

Mrs  B.  The  history  of  the  steam  engine,  from  the  first  rude  attempts 
to  communicate  motion  by  the  elastic  force  of  vapour,  to  the  almost  intel- 
lectual action  of  this  powerful  machine,  as  now  employed,  is  one  which  you 
may  hereafter 'examine  with  much  pleasure  ana  advantage.  Like  the  ship, 
the  clock,.the  watch,  and  all  other  complicated  machines,  it  has  advanced 
by  successive  steps  to  the  state  of  perfection  which  it  has  now  attained. 

Man  could  not  apply  fire  to  the  purpose  of  heating  water  without  having 
his  attention,  in  some  degree,  arrested  by  the  elastic  force  of  steam. 
It  is  known  that  among  the  Greeks,  Hero  of  Alexandria  caused  a  wheel  to 
revolve  by  the  reaction  of  steam,  issuing  from  boiling  water.  The  useful 
application  of  this  agent,  however,  is  altogether  of  modern  origin(l). 


26.  Why  may  a  surface  formed  of  spheres  appear  perfectly  even? 

27.  What  is  sometimes  apparent  in  the  structure  of  a  crystal? 

1.  What  is  observed  respecting  the  invention  of  the  steam  engine? 


ON  THE  STEAM  ENGINE.  267 

Emily.  Then  its  history  must  be  more  perfectly  known  than  that  of  the 
"more  ancient  instruments  ;  and  the  names  of  those  who  have  successively 
improved  it  are  not  lost  with  the  records  of  antiquity,  hut  are  registered 
in  the  list  of  public  benefactors. 

Mrs  JB.  Your  remarks  are  correct.  Our  business  to  day,  however,  will 
not  be  to  learn  the  history  of  the  steam  engine,  but  to  examine  it  in  its 
present  improved  form;  and  should  I  succeed  in  making  you  acquainted  with 
its  structure,  you  will  find  no  difficulty  in  understanding  the  various  changes 
through  which  it  had  previously  passed.  The  engine  which  I  shall  de- 
scribe is  called  Watt's  engine,  as  it  is  to  Mr  Watt,  of  England,  that  we  are 
indebted  for  its  most  valuable  improvements.  In  our  examination  of  the 
steam  engine  it  will  be  necessary  to  recur  to  what  you  have  learnt,  both 
in  your  natural  philosophy  and  your  chemistry,  respecting  the  nature  of 
heat,  and  of  the  elastic  fluids:  you  must  particularly  observe  the  distinc- 
tion which  subsists  between  the  vapours  and  the  gases. 

Caroline.  We  know  that  the  vapours,  by  being  cooled,  may  be  con- 
verted into  liquids;  whilst  the  gases  by  any  ordinary  reduction  of  tem- 
perature will  be  merely  diminished  in  hulk,  still  remaining  in  the  aeriform 
state(2). 

Mrs  B.  What,  therefore,  would  be  the  effect  of  cooling  a  vessel  which 
was  filled  with  steam,  and  closed  so  that  air  could  not  find  admission 
into  it?  , 

Emily.  In  this  case  the  steam  would  be  condensed,  would  assume  a  li- 
quid form,  and  a  vacuum  would  be  produced  within  the  vessel. 

Caroline.  Yes,  and  then,  if  the  vessel  was  not  of  considerable  strength, 
it  would  be  crushed  in,  by  the  pressure  of  the  atmosphere,  like  the  square 
bottles  which  were  broken  when  the  air  they  contained  was  exhausted  by 
means  of  the  air  pump(3). 

Mrs  B.  The  facts  of  the  elasticity  of  steam,  and  its  condensation  by 
cooling,  include  the  elements  of  motion  in  the  steam  engine,  as  improved  by 
Mr  Watt.  This  engine,  unlike  its  predecessors,  acts  independently  of  the 
pressure  of  the  atmosphere;  as,  in  lieu  of  this  pressure,  Watt  substituted  the 
elastic  force  of  steam,  which,  at  the  ordinary  temperature  of  boiling  water, 
is  equal  to  that  of  the  atmosphere,  and  this,  you  know,  is  about  fifteen  pounds 
upon  every  inch  of  surface(4). 

Emily.  The  mechanical  power  of  steam  must  necessarily  be  equal  to 
that  of  the  atmosphere;  for  when  water  boils  in  an  open  vessel,  it  must 
overcome  the  weight  which  is  pressing  upon  it,  and  to  do  this,  must  exert 
a  force  equal  to  that  by  which  its  own  power  is  resisted(5). 

Mrs  B.  With  the  knowledge  of  this  law,  you  will  find  no  other  diffi- 
culty in  understanding  the  action  of  the  steam  engine,  than  that  which  ari- 
ses from  the  necessary  complexity  of  its  mechanical  arrangements.  These 
are  principally  intended  to  regulate  the  admission  of  steam  into  it,  from  the 
boiler,  and  the  discharge  of  this  steam  after  it  has  performed  its  office(6). 

I  have  made  some  diagrams,  to  aid  us  in  explaining  the  operation  of  the 
engine,  and  you  would  find  these  drawings  answer  the  purpose  better  than 
the  machine  itself,  if  we  had  one  at  our  command. 

Caroline.  Undoubtedly ;  for  by  them  you  will  be  able  to  show  us  its 
interior  structure,  which  we  could  not  see  in  the  real  engine, 

Mrs  B.     When  steam  is  employed  for  the  purpose  of  pumping  water, 


2.  Repeat  the  distinction  which  subsists  between  gases  and  vapours. 

3.  What  would  be  the  effect  of  cooling  a  vessel  containing  steam? 

4.  What  are  the  leading  characteristics  of  Mr  Watt's  engine? 

5.  What  proves  the  elastic  force  of  air  and  steam  to  be  equal? 

6.  What  are  many  of  the  moving  parts  of  the  engine  intended  to  regu- 
late? 


268 


CONVERSATIONS  ON  CHEMISTRY. 


of  propelling  a  boat,  or  of  driving  the  machinery  used  in  manufactories,  it 
is  admitted  from  a  boiler  into  a  cylinder,  in  which  it  operates  upon  a  piston. 
The  cylinder  and  piston  are,  in  form,  very  similar  to  those  of  the  common 
air  or  water  pump.  The  piston,  however,  is  without  a  valve(7). 

This  drawing  represents  such  a  piston  within  its  cylinder.  It  is  fitted  to 
the  cylinder  so  perfectly,  that  when  it  is  worked  up  and  down,  no  steam 
can  pass  between  them.  The  drawing  also  shows  the  manner  in  which  the 
steam  is  to  be  admitted  and  discharged,  in  order  to  operate  upon  the 
piston. 


Steam  Cylinder,  JBoiler,  and  Condenser. 


Fig.l. 


I  need  not  explain  to  you  the  design  of  that  part  which  in  the  drawing 
is  marked  A. 

Caroline.  It  is  evidently  the  boiler,  and  the  furnace  for  converting 
the  water  which  it  contains  into  steam. 

JMrs  JB.  And  you  perceive  that  a  pipe,  B,  leads  from  this  boiler,  and 
branches  off,  so  as  to  communicate  with  the  upper  part  of  the  cylinder 
C,  C,  at  the  point  D,  and  with  the  lower  part  at  the  point  E.  The  communi- 
cation with  either  the  upper  or  the  lower  part  of  the  cylinder  may  be  opened 
or  closed  at  pleasure,  by  means  of  the  keys  or  valves,  F  and  G(8). 

Emily.  There  is  no  difficulty  in  perceiving  that  when  F  is  closed  and 
G  open,  the  steam  will  be  admitted  above  the  piston  only;  but  I  should  ap- 
prehend that  if  the  piston,  H,  is  to  move  up  and  down,  and  the  piston  rod  I 
to  pass  freely  through  the  top  of  the  cylinder,  the  steam  must  escape  around 
the  piston  rod,  into  the  atmosphere. 

Mrs  J8.  The  piston  rod  is  made  perfectly  cylindrical,  and  is  kept  steam 
tight,  at  J,. by  passing  through  what  is  called  a  stuffing-  box;  that  is,  a 
box,  or  opening,  stuffed  with  tow,  wool,  or  some  other  elastic  substance. 
The  rod  is  thus  enabled  to  work  freely,  whilst  the  escape  of  steam  is  effect- 
ually prevented(9). 

Caroline.  When  the  steam  is  admitted  at  D,  it  is  of  course  intended 
to  force  the  piston  down;  but  if  the  power  of  the  steam  is  only  equal  to  that" 


7.  Within,  and  upon,  what  does  the  steam  first  operate  ? 

8.  How  is  the  steam  admitted  either  above  or  below  the  piston? 

9.  How  is  the  escape  of  steam  around  the  piston  rod  prevented* 


ON  THE  STEAM  ENGINE.  269 

of  the  pressure  of  the  atmosphere,  the  air  below  the  piston  must  effectually 
prevent  its  descent(lO). 

Mrs  B.  That  certainly  would  he  the  case,  if  means  had  not  been  de- 
vised to  remove  the  air,  and  to  obtain  a  vacuum  under  the  piston.  If  this 
can  be  effected,  the  pressure  of  the  steam  must  cause  the  piston  to  descend, 
and  that  with  a  power  proportioned  to  its  area  or  surface. 

Emily.  Its  tendency  to  descend  must  in  that  case  be  very  great  indeed, 
as  it  will  be  equal  to  a  weight  of  fifteen  pounds  upon  every  square  inch  of 
it.  If  the  cylinder  is  large,  this  power  must  be  enormous  in  amount(ll). 

Mrs  B.  You  may  conceive  some  idea  of  this  force,  when  you  are  in- 
formed, that  it  surpasses  the  weight  of  a  column  of  lead  three  feet  in  height, 
and  of  the  same  diameter  with  the  cylinder,  or  piston,  of  the  engine(12). 

The  mode  by  which  a  vacuum  is  created  in  the  cylinder,  was  invented 
by  Mr  Watt,  and  is  one  of  the  most  important  of  his  many"  improvements. 
You  perceive  that  in  the  drawing  there  is  a  branched  tube,  similar  to  that 
which  is  connected  with  the  boiler,  but  on  the  opposite  side  of  the  cylinder, 
and  that  it  terminates  in  a  vessel  marked  L.  The  first  tube,  B,  is  called 
the  steam  pipe ,  as  it  conducts  the  steam  into  the  cylinder;  the  latter  is 
named  the  eduction  pipe,  and  is  intended  for  the  discharge  of  the  steam, 
after  it  has  acted  upon  the  piston(lS).  The  vessel  L,  into  which  the  steam 
is  conveyed  by  the  eduction,  or  discharge  pipe,  is  called  the  condenser}  it  is 
a  strong  metallic  box,  so  enclosed  that  no  air  can  enter  it(l4). 

Caroline,  And  I  am  not  wise  enough  to  tell  why  the  steam  should  enter 
it,  for,  unless  a  vacuum  could  be  maintained  there,  the  steam  would  be 
no  more  inclined  to  pass  into  it,  than  to  remain  in  the  cylinder;  and  if  it  did 
pass  into  it  and  become  condensed  there,  this  condenser,  after  a  while, 
would  be  filled  with  water.  These  are  difficulties  which  would  place  all 
my  skill  at  defiance;  but  the  philosopher  who  invented  this  apparatus  has, 
of  course,  provided  against  them(  15). 

Mrs  B.  The  small  pump  M,  which  is  placed  upon  the  condenser,  re- 
moves these  difficulties  completely.  It  is  kept  constantly  at  work,  and  ex- 
hausts the  condenser,  both  of  air  and  of  water;  and  thus  produces  and  main- 
tains a  vacuum,  the  necessity  of  which  you  have  had  the  good  sense  to  fore- 
see. This  pump  is  technically  called  the  air  pump.  It  does  not  differ 
from  the  common  pump,  excepting  in  the  accuracy  with  which  it  is  made(16). 

Caroline.  I  wonder  that  I  had  not  understanding  enough  to  perceive  the 
use  of  it,  in  the  conspicuous  situation  which  it  occupies. 

Emily.  Does  not  the  heat  which  the  steam  carries  with  it  into  the  eon- 
denser,  interfere  with  the  condensation;  or  rather,  I  should  ask,  in  what 
way  is  this  interference  prevented? 

Mrs  B.  Just  as  it  is  prevented  in  the  common  still,  the  worm  of  which 
is  kept  surrounded  by  cold  water.  The  condenser  stands  in  a  cistern,  or 
vessel  N,  called  the  cold  -water  -well.  On  board  of  steam  boats  this  -well  is 
supplied  by  the  water  of  the  river,  and  on  land  from  any  convenient  source. 
To  render  the  condensation  still  more  rapid,  a  stream  of  cold  water,  O,  is 
.allowed  to  run  from  the  well  into  the  condenser(17). 

Caroline.     The  air  pump,  then,  must  be  sufficiently  large  to  pump  out 


10.  If  the  piston  had  air  on  one  side  and  steam  on  the  other,  what  would 
be  the  result? 

11.  What  if  steam  was  on  one  side  and  a  vacuum  on  the  other? 

12.  To  the  weight  of  what  mass  of  lead  would  this  power  be  equal? 

13.  What  are  the  steam  and  eduction  pipes  intended  to  effect? 

14.  What  kind  of  vessel  is  that  which  is  called  the  condenser? 

15.  What  is  necessary  to  cause  the  steam  jto  pass  into  it? 
16    What  are  the  situation  and  use  of  the  air-pump? 

17.   In  what  way  is  the  steam  condensed  in  the  condenser? 
X  2 


270  CONVERSATIONS  ON  CHEMISTRY. 

the  air,  the  water  which  runs  in  from  the  cold  water  well,  and  that  which 
is  produced  by  the  condensation  of  the  steam.  By  what  means  is  this  air- 
pump  kept  continually  at  work? 

Mrs  JB.  The  air  pump  and  all  the  other  moving  parts  of  the  engine  are 
acted  upon  hy  the  engine  itself,  and  of  course  some  portion  of  its  power  is 
expended  in  working  them(18).  This  will  be  better  understood  by  you 
after  I  have  shown  and  explained  to  you  a  more  perfect  drawing  of  the 
whole  engine.  Our  present  sketch,  however,  will  enable  you  to  trace  the 
action  of  the  engine  more  readily  than  the  complex  figure  necessary  to  show 
its  general  structure. 

Emily.  You  have  so  clearly  explained  the  use  of  the  condenser,  that 
with  a  little  study,  we  might  almost  venture  to  trace  the  operation  of  the 
engine,  without  further  aid;  but  whilst  we  have  you  for  a  guide,  we  have 
not  the  temerity  to  venture  alone  along  a  path  which  we  have  never  explored. 

Mrs  B.  We  have  now  advanced  sufficiently  far  to  set  our  engine  at 
work,  at  least  in  imagination.  The  kind  of  machine  which  I  am  describ- 
ing to  you,  is  sometimes  called  the  double  acting  engine.  It  is  so  named 
because  the  piston  is  forced  upwards,  with  the  same  power  with  which  it  is 
made  to  descend.  The  steam,  as  I  have  before  intimated,  being  alternately 
admitted  to,  and  removed  from,  each  side  of  it. 

You  perceive  that  the  eduction  pipe,  K,  may  allow  of  a  communication 
between  the  condenser,  and  either  end  of  the  cylinder,  accordingly  as  the 
vents,  or  valves,  at  P  and  Q,  are  opened  or  closed.  These  vents  we  will 
hereafter  simply  pall  valves,  as  they  actually  are  such  in  the  working  engine. 
Suppose  now  that  the  whole  four  valves,  F,  G,  and  P,  Q,  were  opened  at 
the  same  time,  whilst  the  water  in  A  was  kept  boiling,  what  would  be  the 
result? 

Emily.  The  steam  would  then  rush  into  the  cylinder  at  both  ends,  and 
press  equally  on  each  side  of  the  piston;  and  from  the  cylinder  it  would 
pass  through  both  branches  of  the  eduction  pipe  into  the  condenser. 

Mrs  B.  Yes;  and  it  would  pass  up  from  the  condenser  through  the  valves 
of  the  air-pump,  blowing  out  the  air  before  it  and  occupying  its  place(  19). 
This  is  in  fact  the  first  step  taken  when  such  an  engine  is  to  be  set  at  work; 
and  this  operation  is  called  blowing"  through(%0}.  After  blowing  through, 
that  is,  filling  the  whole  interior  of  the  engine  with  steam,  can  you  tell  me 
what  would  be  the  consequence  of  closing  the  valves  F  and  Q> 

Caroline.  Allow  me  to  consider  a  moment.  The  steam  would  continue 
to  enter  through  the  valve  G,  into  the  upper  part  of  the  cylinder,  where  it 
would  be  confined  by  the  closing  of  the  valve  Q.  I  suppose,  too,  that  the 
valve  P  being  open,  and  the  valve  F  shut,  the  steam  would  rush  from  under 
the  piston,  into  the  condenser,  where  it  would  be  converted  into  water;  this 
would  necessarily  produce  a  vacuum  under  the  cylinder,  and  the  piston 
would  be  forced  down(21). 

Mrs  B.  Perfectly  well  explained.  After  understanding  how  the  piston 
and  its  rod  are  forced  down,  you  will  find  little  difficulty  in  perceiving  how 
they  may  be  elevated  by  the  same  means,  and  with  a  power  equal  to  that  of 
their  descent.  Only  suppose  the  valves  F  and  Q  to  be  opened,  and  P  and  G 
to  be  closed;  and  you  perceive  that  the  steam  would  then  be  admitted  under 
the  piston,  whilst  that  which  had  forced  it  down  would  rush  through  the 
valve  Q,  into  the  condenser,  and  cause  a  vacuum  to  be  instantly  formed  above 
the  piston.  Thus  situated,  it  would  be  carried  to  the  top  of  the  cylinder 
hy  the  elasticity  of  the  steam,  and  when  there,  if  the  open  valves  are  again 


18.  What  is  said  of  the  means  of  giving  motion  to  the  air-pump? 

19.  What  would  be  the  effect  of  opening  all  the  valves? 

20.  What  is  this  operation  denominated? 

21.  Explain  the  steps  necessary  to  set  the  engine  in  motion? 


ON  THE  STEAM  ENGINE.  271 

closed,  and  the  closed  valves  opened,  it  will  again  descend  with  equal 
power(22). 

Emily.  I  had  entertained  the  idea  that  the  operation  of  the  engine  was 
in  some  way  connected  with  the  pressure  of  the  atmosphere,  but  I  now  per- 
ceive that  the  effect  of  this  pressure  must  always  he  to  retard  its  action,  and 
that  it  would  actually  stop,  if  more  air  entered  than  the  air  pump  could 
exhaust(23). 

Caroline.  The  passing  of  the  piston  up  and  down  I  now  perfectly  under- 
stand, but  still  I  do  not  perceive  how  this  is  to  propel  boats,  drive  carriages, 
pump  water,  and  turn  almost  all  kinds  of  machinery.  I  thought  that  the 
force  of  the  steam  effected  all  this;  but  we  seem  to  have  destroyed  the 
steam  in  the  very  act  of  moving  the  piston  and  its  rod  up  and  down. 

J\frs  B.  And  to  produce  this  motion  of  the  piston  is  all  that  is  required 
of  it.  If  you  will  supply  the  machinist  with  powerful  motion  of  any  kind, 
he  well  knows  how  to  give  to  it  such  a  direction  as  shall  serve  all  his  pur- 
poses. Do  you  not  perceive  that  if  the  piston  rod  was  attached  to  the  end 
of  the  handle  of  a  pump  it  would  cause  it  to  vibrate,  as  a  man  does,  when  he 
uses  it  for  the  purpose  of  raising  water?  If  a  rotary  motion  is  required,  it 
can  be  obtained  from  the  vibration  of  the  piston  rod,  just  as  the  wheel  for 
spinning  flax  is  made  to  revolve  through  the  medium  of  a  crank,  by  merely 
raising  and  lowering  the  foot(24). 

Emily.  I  confess  that  I  also  was  impressed  with  an  idea  that  the  force 
of  steam  was  applied  in  some  way  more  direct  than  that  which  you  have  de- 
scribed. I  now  perceive,  however,  that  it  is  merely  a  substitute  for  the 
power  of  men  or  horses,  and  that  it  acts,  as  they  generally  do,  through  the 
intermedium  of  levers  and  wheels. 

Caroline.  The  part  marked  R,  which,  I  believe,  is  called  the  safety 
valve,  you  have  not  described.  I  have  always  conceived  this  to  be  one  of 
the  most  important  appendages  to  the  steam  engine. 


Safety  Valve. 


Fig.  2. 


Mrs  B.  And  so  it  is,  as  its  name  indicates.  With  the  nature  of  valves, 
generally,  you  are  acquainted,  and  know  that  they  are  of  different  forms. 
The  safety  valve  is  in  form  similar  to  the  stopper  of  a  decanter,  but  more 
conical.  This  is  a  separate  drawing  of  it,  in  which  A  shows  the  upper 
part  of  the  boiler,  and  B  the  valve.  You  will  perceive  from  the  drawing 
that  if  the  steam  within  the  boiler  A  becomes  very  elastic,  it  will  press 
upon  the  lower  end  of  the  valve  B,  and  if  the  weight  C,  which  tends  to 
keep  it  down,  is  not  too  great,  it  will  be  raised,  and  the  steam  escape, 
without  endangering  the  boiler(25). 

Emily.  In  the  low  pressure  engine,  the  weight,  I  suppose,  is  equal  to 
fifteen  pounds  upon  each  square  inch  of  the  lower  end  of  the  valve,  so 
that  its  force  may  amount  to  the  same  as  that  of  the  atmosphere. 


22.  By  what  means  is  the  piston  made  to  ascend? 

23.  What  effect  would  the  admission  of  air  produce? 

24.  How  does  the  engine  operate  in  moving  other  machinery? 

25.  Describe  the  structure  and  operation  of  the  safety  valve,  i 


272  CONVERSATIONS  ON  CHEMISTRY. 

Mrs  B.  By  no  means.  The  atmosphere  itself  has  this  force,  and  an 
additional  -weight  of  fifteen  pounds  upon  every  inch  would  resist  the  pres- 
sure of  the  steam  until  it  became  equal  to  that  of  two  atmospheres.  The 
weight  upon  each  square  inch  of  the  valve  should  not  exceed  three  or 
four  pounds?  but  this  amount  is  necessary  in  order  to  give  to  the  steam  a  de- 
gree of  elasticity  sufficient  to  blow  out  against  the  atmosphere,  with  such 
a  force  as  completely  to  counteract  its  tendency  to  pass  into  the  engine(26.) 

Emily.  Was  there  not  a  machine  called  the  Atmospheric  Engine  which 
was  in  use  before  the  improvements  made  by  Mr  Watt? 

Mrs  B.  Yes:  and  it  was  a  desire  to  improve  the  operation  of  this  en- 
gine, that  led  Mr.  Watt  to  the  adoption  of  those  devices  by  which  he  has 
furnished  us  with  a  power  so  efficient  and  so  manageable.  The  Atmospheric 
Engine  was  invented,  in  England,  about  the  commencement  of  the  last  cen- 
tury by  Newcomen.  He  used  a  cylinder  and  a  piston,  but  the  whole  mo- 
tive power  of  his  machine  was  derived  from  the  pressure  of  the  atmos- 
phere(27). 

Caroline.  Then  I  think  it  could  not  with  much  propriety  be  called  a 
steam  engine. 

Mrs  B.  It  was  as  truly  a  steam  engine  as  those  now  in  use.  Steam  was 
employed  in  it  to  create  a  vacuum,  without  which  the  pressure  of  the  at- 
mosphere could  not  have  been  rendered  efficient.  In  Newcomen's  engine 
there  was  a  boiler,  and  a  steam  pipe  leading  from  it  into  the  lower  part  of 
a  cylinder,  somewhat  in  the  manner  of  the  lower  pipe  E,  in  our  first  draw- 
ing. The  upper  part  of  the  cylinder  was  not  closed,  but  the  air  was  freely 
admitted  to  press  upon  the  surface  of  the  piston(28).  On  turning  again  to 
the  drawing,  you  may  suppose  the  piston  H  to  be  at  the  bottom  of  the  cy- 
linder C,  C,  and  to  fit  it  air  tight;  can  you  tell  me  what  force,  besides  the 
weight  of  the  piston  itself,  would  be  required  to  raise  it  in  the  cylinder, 
provided  neither  air  or  steam  were  admitted  below  it? 

Emily.  In  that  case  the  whole  weight  of  the  atmosphere  must  be  lifted, 
as  there  would  be  a  vacuum  beneath  the  piston.  The  power,  therefore,  must 
be  proportioned  to  the  diameter,  or  area,  of  the  piston(29). 

Mrs  B.  But  were  we  to  admit  steam  under  the  piston,  from  the  boiler 
A,  would  this  difficulty  exist?  , 

Emily.  Certainly  not;  because  the  steam,  by  its  elasticity,  would  be  a 
counterpoise  to  the  weight  of  the  atmosphere.  The  piston  might  then  be 
readily  raised  to  the  top,  as  the  cylinder  would  be  filled  with  steam(SO). 

Caroline.  Yes,  and  if  this  steam  was  then  condensed,  there  would  be  a 
vacuum,  into  which  the  piston  would  be  forced  by  the  weight  of  the  air. 

Mrs  B.  By  applying  cold  water  to  the  cylinder,  the  steam  within  it  would 
be  condensed;  and  this  was  done  in  Newcomen's  engine  at  every  stroke  of 
the  piston(Sl).  This  instrument,  although  very  useful,  was  also  very  defec- 
tive; but  as  my  whole  design  was  to  give  you  some  idea  of  the  way  in  which  the 
pressure  of  the  atmosphere  was  employed  in  it,  I  shall  not  at  present  take 
any  further  notice  either  of  its  merits  or  its  defects. 

Caroline.  Some  of  the  latter,  at  least,  are  very  apparent.  It  must  have 
wasted  a  great  deal  of  steam  in  heating  the  cylinder  at  every  stroke,  and 
its  power  was  exerted  in  one  direction  only(32). 


26.  To  what  should  the  load  upon  the  safety  valve  amount? 

27.  By  whom,  and  at  what  period  was  the  atmospheric  engine  invented? 

28.  What  was  the  construction  of  the  cylinder,  and  where  was  the  steam 
admitted? 

29.  By  what  power  would  the  raising  of  such  a  piston  be  opposed? 

30.  How  would  the  admission  of  steam"  obviate  this  difficulty? 

31.  How  was  the  pressure  of  the  atmosphere  made  to  operate?. 

32.  What  two  defects  are  mentioned,  as  belonging  to  this  engine? 


ON  THE  STEAM  ENGINE.  273 

Mrs  B.  You  are  now  prepared  to  examine  my  drawing  of  a  steam  en- 
gine, with  most  of  the  working  parts  attached  to  it.  You  will  find  that 
some  of  them  are  arranged  differently  from  those  in  our  first  sketch,  as  this 
larger  drawing  is  a  more  perfect  representation  of  the  actual  form  of  the 
engine  as  applied  to  use.  But  still  you  must  not  expect  to  find  it  an  exact 
likeness  of  any  one  which  you  have  seen.  To  every  tube  and  valve  I  have 
assigned  such  a  position  as  I  thought  would  enable  you  most  readily  to  un- 
derstand it.  On  board  of  steam  boats,  and  in  manufactories,  the  parts  are 
crowded  together,  and  distorted  in  various  ways,  for  the  purpose  of  sav-' 
ing  room,  or  of  obtaining  other  advantages(SS). 

Caroline.  Your  first  drawing  has  made  the  manner  in  which  the  steam 
operates  so  plain,  that  we  cannot  find  any  difficulty  in  following  you  in  your 
further  developments  of  this  beautiful  machinery. 

Mrs  B.  You  will,  at  the  first  glance,  perceive  the  resemblance  between 
this  more  full  drawing  (fig.  3)  and  the  former,  so  far  as  the  structure  of  the 
cylinder,  and  the  operation  of  the  steam  are  concerned.  To  all  of  its  cor- 
responding parts  I  have  affixed  the  same  letters.  You  will,  therefore,  rea- 
dily trace  their  connexion. 

Emily.  The  form  itself  is  but  little  altered,  but  I  perceive  that  at  G,  P, 
and  P,  Q,  you  have  placed  valves  for  the  admission  and  discharge  of  the 
steam;  and  that  they  appear  to  be  similar  in  shape  to  the  safety  valve  upon 
the  boiler. 

Mrs  B.  They  are  of  the  same  kind,  and  are  called  puppet  valves.  The 
casing  which  surrounds  each  of  them  is  called  a  steam  box.  They  are 
opened  and  closed  by  means  of  a  small  rod  passing  through  a  stuffing  box, 
like  that  surrounding  the  piston  rod.  You  perceive  the  loops  upon  the  tops 
of  each  of  these  rods;  by  these  they  are  raised  and  lowered.  This  is  effect- 
ed, at  the  moment  required,  by  apparatus  worked  by  the  engine  itself(34). 

Emily.  The  part  S,  which  I  know  is  called  the  lever  or  beam,  is  made 
to  vibrate  by  means  of  the  piston  rod,  the  upper  end  of  which  is  attached  to 
it.  What  is  the  particular  end  answered  by  this  large  lever? 

Mrs  B.  The  intention  of  this  lever  is  to  communicate  the  motion  gene- 
rated in  the  cylinder,  to  any  machinery  which  is  to  be  operated  upon.  Thus 
if  it  is  designed  to  raise  water  from  a  well  or  from  a  mine,  a  piston  rod,  T, 
may  be  attached  to  the  opposite  end  of  the  lever,  and  made  to  work  a  pump 
below  it.  I  have  not  drawn  the  pump,  as  you  are  well  acquainted  with  its 
structure,  and  I  have  avoided  multiplying  parts  unnecessarily (35). 

Caroline.  In  this  case  the  lever  becomes  the  pump  handle  and  the  en- 
gine the  power  which  works  it.  This  removes  all  the  mystery  about  apply- 
ing steam  to  the  raising  of  water. 

Mrs  B.  When  a  rotary  motion  is  required,  as  in  the  paddle  wheels  of 
steam  boats,  and  in  mills  of  most  kinds,  it  is  obtained  from  that  of  thejly 
•wheel  V:  this  is  caused  to  revolve  by  the  action  of  the  rod  W,  which  acts 
upon  the  crank  X.  A  wheel  of  this  description,  or  something  which  an- 
swers a  similar  purpose,  is  attached  to  all  steam  engines,  and  to  many 
other  machines,  in  order  to  regulate  their  motion.  In  large  engines,  the 
fly  wheel  may  weigh  several  tons,  and  this  great  weight  is  absolutely  ne- 
cessary to  their  steady  and  uniform  action(36). 

Emily.  But  does  not  this  waste  a  considerable  part  of  the  power  of  the 
engine?  It  must  require  no  little  force  to  move  so  heavy  a  wheeL 


33.  What  is  said  respecting  the  drawing  and  the  actual  engine? 

34.  What  is  said  of  the  valves  in  the  steam  and  eduction  pipes? 

35.  What  is  the  purpose  answered  by  the  lever-beam? 

36.  What  vs  remarked  respecting  a  rotary  motion  andyfy  wheel? 


•i 

274  CONVERSATIONS  ON  CHEMISTRY. 


DESCRIPTION 


WATT'S  LOW  PRESSURE  STEAM  ENGINE. 

-, ' 

A.  The  BOILER,  the  dark  part  representing  steam. 

B.  The  STEAM   or  INDUCTION  PIPE,  conducting  steam  into  the  cylinder. 

C.  The  CTLINDER,  communicating  with  the  boiler  both  above  and  below. 

D.  The  branch  of  the  steam  pipe  opening  into  the  upper  end  of  the  cylinder. 

E.  The  branch  opening  into  the  lower  end. 

F.  The  LOWER  STEAK  VALVE,  represented  as  open. 

G.  The  UPPER  STEAM  VALVE,  represented  as  closed. 

H.  The  PISTON,  which  is  operated  upon  by  the  steam  on  each  side  alter- 
nately, causing  the  motion  of  the  piston  rod  and  the  lever  beam. 

I.    The  PISTON  ROJD,  attached  to  the  piston,  and  to  the  beam. 

J.    The  STUFFING  BOX,  through  which  the  piston  rod  works  steam  tight. 

K.  The  EDUCTION,  of  DISCHARGE  PIPE,  by  which  the  steam  is  conveyed  into 
the  condenser,  after  it  has  performed  its  office  in  the  cylinder. 

L.   The  CONDENSER,  surrounded  by  the  cold  water  well. 

M.  The  AIR  PUMP,  to  keep  the  condenser  exhausted  of  air  and  water. 

N.  The  COLD  WATER  WELL,  which  must  be  constantly  supplied  with  fresh 
water. 

O.   A  stream  of  water,  running  from  the  well  into  the  condenser. 

P.  The  LOWER  VALVE  or  THE  EDUCTION  PIPE,  represented  as  closed. 

Q.   The  UPPER  EDUCTION  VALVE,  represented  as  open. 

R.  The  SAFETT  VALVE,  with  its  lever  and  weight. 

S.  The  LEVER  BEAM,  caused  to  vibrate  by  the  piston  rod. 

T  A  PUMP  ROD,  which  may  be  attached  to  a  pump  for  raising  water  from  a 
well  or  mine. 

V.  The  FLY  WHEEL,  which  serves  to  equalize  and  regulate  the  motion. 

W.  The  CRANK  ROD,  or  SHACKLE  BAR,  serving  to  give  motion  to  the  fly  wheel. 

X.  The  CRANK,  acted  upon  by  the  rod  and  lever  beam. 

Y.  COCKS  to  ascertain  the  height  of  the  water  in  the  boiler. 

Z  Z.  Jointed  levers  which  form  the  PARALLEL  MOTIOIT. 

•"-••:    •**;;  ?T4f    .f 


ON  THE  STEAM  ENGINE. 


275 


276  CONVERSATIONS  ON  CHEMISTRY. 

Mrs  B.  The  loss  of  power  is  but  trifling,  amounting  to  little  more  than 
the  friction  of  the  axle;  for  the  wheel,  by  its  momentum,  gives  back  again  the 
power  which  it  receives,  whilst  it  prevents  that  jerking  from  the  vibration 
of  the  piston  and  the  beam,  which  would  otherwise  soon  destroy  the  engine. 

Caroline.  The  piston  rods,  both  of  the  cylinder  and  of  the  air-pump, 
are  attached  to  jointed  levers,  and  through  them  to  the  beam.  I  have  heard 
these  jointed  levers  called  the  parallel  motion;  will  you  be  good  enough  to 
describe  to  us  their  nature  and  use? 

Mrs  B.  This  parallel  motion  was  a  most  happy  contrivance  of  Mr  Watt. 
You  perceive  that  as  the  piston  rods  pass  through  a  stuffing  box  in  the  caps 
of  the  cylinder,  they^  require  to  be  carried  up  and  down  vertically.  The  end 
of  the  lever  vibrates  in  a  curve,  and  would  therefore  give  to  the  piston  rods 
a  rocking  motion,  which  must  bend  or  break  them:  this  the  parallel  motion 
prevents(37).  I  have  made  a  sketch  which  will  serve  to  show  you  the  prin- 
ciple upon  which  it  acts — here  it  is. 

The  Parallel  Motion. 
Fig.  4. 


In  this  drawing,  A  is  one  end  of  the  lever  of  the  engine,  which  is  connect- 
ed to  a  second  lever  B,  by  means  of  a  jointed  piece  C,  to  the  middle  of  which 
jointed  piece  the  piston  rod  is  attached. 

Emily.  That  is  very  simple  and  beautiful.  I  see  plainly  how  it  operates. 
As  the  main  lever  A  draws  one  end  of  the  connecting  joint  C  in  the  curve  E  F, 
the  lever  B,  which  is  attached  to  the  building  at  G,  draws  the  opposite  end 
of  it  in  the  reverse  curve  H  I,  the  consequence  of  which  is,  that  the  middle 
of  the  piece  C,  to  which  the  piston  rod  is  attached,  passes  up  and  down  in  a 
vertical  line(38). 

•Mrs  B.  There  are  several  other  equally  ingenious  appendages  to  the 
steam  engine.  One  of  these  is  called  a  governor,  as  it  is  intended  to  govern 
the  velocity  of  the  engine's  motion.  When  the  engine  begins  to  move  too 
rapidly,  the  governor  acts  upon  a  valve  which  lessens  the  aperture  by  which 
the  steam  is  admitted,  and  this  diminishes  the  cause  of  motion(39). 

Levers,  which  are  raised  up  and  depressed  by  what  is  called  an  eccentric, 
which  is  affixed  to  the  shaft  of  the  fly  wheel,  are  now  employed  to  open  and 
close  the  valves  in  the  steam  and  the  eduction  pipes.  I  cannot,  however, 
explain  all  these  to  you  at  present,  as  it  would  detain  us  too  long  from  our 
ehemistry(40). 

Caroline.  You  have  explained  enough  to  interest  us  very  highly  in  the 
subject;  and  if,  without  too  much  sacrifice  of  time,  you  could  inform  us  in 


37.  For  what  purpose  is  the  parallel  motion  used? 

«J8.   Describe  the  structure  and  operation  of  this  part  of  the  engine? 

89.   What  is  the  design  of  the  part  called  a  governor? 

40.  What  is  said  of  the  opening  and  closing  of  the  valves? 


ON  THE  STEAM  ENGINE. 


277 


what  the  high  pressure  engine  differs  from  that  which  you  have  described, 
it  would  gratiiy  us  very  much. 

Mrs  B.  I  will  do  so  with  pleasure;  it  is  a  point,  indeed,  which  must  not 
be  altogether  omitted,  although  I  can  give  you  b*ut  a  mere  outline. 

You  are  aware  that  when  water  is  confined  in  a  close  vessel,  its  tempera- 
ture may  be  increased  above  the  ordinary  boiling  point,  and  that  the  force 
of  its  vapour  will  be  proportionably  increased. 

Carotene.  That  we  understand  very  well,  and  know  that  it  may  be  so 
heated  that  scarcely  any  vessel,  however  strong,  can  resist  its  force(4l). 

Mrs  B.  Suppose  that  in  Mr  Watt's  engine  you  were  to  omit  the  cold 
water  well,  the  condenser,  and  the  air  pump;  what  then  would  become  of 
the  steam,  when  either  of  the  valves  P  or  Q  was  opened? 

Emily.  In  that  case  the  steam  would  blow  off  into  the  atmosphere  at 
every  stroke  of  the  engine.  But  so  situated  I  do  not  see  how  the  engine 
could  continue  to  work,  because  the  atmosphere  would  be  admitted  into  the 
cylinder,  and  counteract  the  pressure  of  the  steam  on  the  opposite  side  of 
the  piston(42). 

Mrs  B.  But  if- the  boiler  was  made  sufficiently  strong,  and  the  water  so 
highly  heated  that  its  vapour  operated  with  a  power  equal  to  that  of  five  at- 
mospheres, or  seventy-five  pounds  upon  the  square  inch,  what  would  then 
be  the  consequence? 

Emily.     In  that  case  the  excess  of  the  pressure  of  Illustration  of  the  Loto 
the  steam  over  that  of  the  air  would  be  sixty  pounds     Pressure  Engine. 
upon  every  square  inch,  and  the  engine  would  work 
with  great  power,  and  eertainly  it  might  then  be 
made  much  smaller  than  the  low  pressure  engine, 
and  yet  have  equal  power(43). 

Caroline.  But  still  there  would  be  the  loss  of  a 
whole  atmosphere  which  the  condenser  and  air  pump 
would  save. 

Mrs  B.  The  air  pump,  you  must  recollect,  not 
only  saves,  but  also  expends  power,  as  it  requires 
considerable  force  to  work  it;  whilst  it  also  renders 
the  engine  much  more  complex  and  expensive.  The 
engines  used  upon  rail  roads  are  all  of  the  high 
pressure  kind,  as  they  could  not  carry  with  them  a 
supply  of  cold  water  to  condense  their  steam;  and 
they  usually  work  with  a  pressure  as  great  as  that 
of  which  I  have  spoken(44). 

1  have  here  an  instrument  by  which  you  can  see 
the  effects  of  elastic  steam  in  overcoming  the  pres- 
sure of  two  atmospheres.  It  is  not  safe  to  carry  the 
experiment  beyond  this,  as  the  vessel  which  I  use 
is  of  glass. 

Caroline.  I  should  have  apprehended  some  dan- 
ger of  bursting  it  even  with  the  power  of  which 
you  speak. 

Mrs  B.  I  have  repeatedly  tried  it,  without  ac- 
cident, and  do  not  doubt  its  capacity  to  raise  a  still 
greater  weight. 

The  glass  tube,  or  cylinder,  A,  has  an  area  of  about 


Fig.  5. 


41.  What  is  the  effect  of  confining  water,  and  heating  it  highly? 

42.  What  would  be  the  effect  of  removing  the  condenser? 

43.  Suppose  the  steam  to  be  equal  in  its  pressure  to  five  atmospheres, 
with  what  power  would  it  act  in  the  high  pressure  engine? 

44.  For  what  purpose  are  these  engines  peculiarly  adapted? 


278  CONVERSATIONS  ON  CHEMISTRY. 

an  inch.  A  piston  fits  closely  in  it,  and  the  bottom  part,  B,  is  made  globu- 
lar, and  contains  water.  On  the  top  of  the  piston  I  have  placed  a  weight,  C, 
of  fifteen  pounds,  which  added  to  that  of  the  air  will  exact  a  power  of  thirty 
pounds  in  order  to  raise  the  piston. 

I  will  now  place  the  bulb  over  the  chaffing  dish  of  coals,  and  allow  it  to 
remain  until  you  see  the  weight  forced  up  by  the  steam(45). 

Caroline.  Will  it  be  necessary  to  double  the  temperature  of  the  water 
in  order  to  double  the  elasticity  of  the  steam? 

•Mrs  B.  By  no  means;  it  only  requires  an  elevation  of  temperature  of  be- 
tween thirty  and  forty  degrees  to  double  the  elasticity  of  the  vapour  from 
boiling  water.  The  elasticity  will  be  again  doubled  by  a  similar  increase 
of  temperature,  and  will  be  equal  to  four  atmospheres  before  it  arrives  at 
300°(46). 

Emily.  See,  Caroline,  the  piston  is  now  rising  with  the  heavy  weight 
upon  it.  That  is  a  very  satisfactory  experiment;  and  the  more  remarkable 
as  being  performed  in  so  fragile  a'vessel  as  one  of  glass. 

Mrs  B.  It  is  now  time  to  adjourn  for  the  evening;  and  you  must  not 
permit  your  thoughts  upon  steam  to  drive  from  your  recollection  that  when 
we  next  meet,  our  subject  is  to  be  organic  chemistry. 


CONVERSATION  XXVIII. 

ON  ORGANIZED  BODIES,  AND  VEGETABLE  CHEMISTRY. 

Organs  of  Animals  and  Vegetables.  Composition  of  Organic  Substances. 
Chemical  Affinity  controlled  by  Vitality.  Destructive  Distillation,  and 
Spontaneous  Decomposition.  Proximate  and,  Remote  Principles.  -  Vege- 
table Principles  divided  into  three  classes.  List  of  some  of  them.  Vege- 
table Acids, — Oxalic,  Tartaric,  Citric,  Benzole,  Gallic,  &c.  Formation 
of  Ink.  Vegetable  Alkalies;  Morphia  and  J\"arcotine;  Quinia  and  Cin- 
chonia.  Oils,  Fixed,  Drying,  Volatile  or  Essential.  Camphor.  Resins. 
Varnishes.  Amber.  Caoutchouc  or  Gum-elastic.  Wax.  Bitumens. 
JVaphtha.  Petroleum.  Mineral  Tar.  Pitcoal.  Anthracite.  Coke. 

Mrs  B.  We  have  hitherto  treated  only  of  the  simplest  combinations  of 
elementary  substances,  such  as  alkalies,  earths,  acids,  salts,  &c. ;  all  of 
•which  belong  to  the  mineral  kingdom.  It  is  time  now  to,  turn  our  attention 
to  a  more  complicated  class  of  compounds,  that  of  ORGANIZED  BODIES, 
which  will  furnish  us  with  a  new  source  of  instruction  and  amusement. 

Emily.  By  organized  bodies,  I  suppose  you  mean  the  vegetable  and  ani- 
mal creation.  I  have,  however,  but  a  very  vague  idea  of  the  word  organ- 
ization, and  I  have  often  wished  to  know  more  precisely  what  it  means. 

Mrs  B.  Organized  bodies  are  such  as  are  endowed  by  nature  with  vari- 
ous parts,  peculiarly  constructed,  and  adapted  to  perform  certain  functions 
connected  with  life.  Mineral  compounds  are  formed  by  the  simple  effect 
of  mechanical  or  chemical  attraction,  and  may  appear  to  be,  in  some  measure, 
the  productions  of  chance;  but  organized  bodies  bear  the  most  striking 
and  impressive  marks  of  design,  and  are  eminently  distinguished  by  the  pos- 
session of  that  unknown  principle  called  life;  a  principle  from  which  the 
various  organs  derive  the  power  of  exercising  their  respective  functions(l). 


45.  Describe  the  experiment  showing  the  elastic  force  of  steam. 

46.  What  elevation  of  temperature  doubles  the  elasticity  of  steam  ? 
1.  What  are  organs,  and  how  are  organized  bodies  distinguished? 


ON  ORGANIZED  BODIES.  279 

Caroline.  But  in  what  manner  does  life  enable  these  organs  to  perform 
their  several  functions? 

Mrs  B.  That  is  a  mystery  which,  it  is  most  probable,  the  Creator  never 
intended  that  we  should  be  able  to  unfold.  We  must,  therefore,  content 
ourselves  with  examining  the  effects  of  this  principle:  as  respects  the  cause, 
we  have  been  able  only  to  give  it  a  name,  without  attaching  any  other  mean- 
ing to  it,  than  the  vague  and  unsatisfactory  idea  of  an  unknown  agent(2). 

Caroline.     And  yet  I  think  I  can  form  a  very  correct  idea  of  life. 

Mrs  B.      Pray  let  me  hear  how  you  would  define  it. 

Caroline.  It  is,  perhaps,  more  easy  to  conceive  than  to  express  the 
idea: — let  me  consider — Is  not  life  the  power  which  enables  both  the  animal 
and  vegetable  creation  to  perform  the  various  functions  which  nature  has 
assigned  to  them? 

Mrs  B.  I  have  nothing  to  object  to  your  definition;  but  you  will  allow 
me  to  observe,  that  you  have  only  mentioned  the  effects  which  the  unknown 
cause  produces,  without  giving  us  any  notion  of  the  cause  itself. 

Emily.  Yes,  Caroline,  you  have  told  us  what  life  does,  but  you  have  not 
told  us  what  it  is. 

Mrs  B.  We  may  study  its  operations;  but  we  should  puzzle  ourselves 
to  no  purpose  by  attempting  to  form  an  idea  of  its  real  nature. 

The  organized  bodies,  which  constitute  the  animal  and  vegetable  king- 
doms, contain  a  vast  number  of  different  compounds,  which  are  nearly  all 
produced  by  the  union  of  the  same  elementary  principles.  Vegetables  con- 
sist essentially  of  carbon,  hydrogen  and  oxygen;  and  the  same  substances, 
with  the  addition  of  nitrogen,  are  the  principal  constituents  of  the  most  im- 
portant compounds  found  in  the  animal  creation(S). 

Caroline.  But  these  are  not  the  only  substances  existing  in  these  bodies, 
as  lime  and  potash  and  phosphorus  have  all  been  mentioned  as  procured 
from  them. 

Mrs  B.  To  your  list  you  might  also  add  sulphur,  iron,  silex,  and  other 
substances  contained  in  the  soil,  from  which  all  organized  beings  primarily 
derive  their  nourishment.  But  although  these  are  essential  to  certain  parts 
of  particular  vegetables  and  animals,  animalization  and  vegetation  may,  to  a 
certain  extent,  exist  without  them(4).  i 

The  organs  with  which  organized  beings  are  endowed,  select  and  arrange 
those  constituent  principles,  and  form  them  into  the  different  kinds  of  juices 
and  solids  which  constitute  vegetable  and  animal  substances,  in  all  their 
varieties(S). 

Emily.  And  are  not  these  combinations  always  regulated  by  the  laws  of 
chemical  attraction? 

Mrs  B.  The  organs  of  animals  and  of  plants  cannot,  certainly,  force 
principles  to  combine  which  have  no  attraction  for  each  other;  but  yet  they 
control  the  combinations  which  take  place,  by  bringing  these  principles 
into  contact  in  such  proportions  as  will,  by  their  chemical  combination, 
form  the  various  organic  products,  instead  of  uniting  according  to  those 
laws  of  simple  affinity  which  they  would  obey,  if  uninfluenced  by  these 
organs  of  vitality(6). 

Caroline.  We  may  then  consider  each  of  these  organs  as  a  curiously 
constructed  apparatus,  adapted  to  the  performance  of  a  particular  chemical 
process. 


2.  Are  we  in  any  degree  acquainted  with  the  principle  of  life? 

3.  What  are  the  principal  constituents  of  vegetable  and  animal  sub- 
stances? 

4.  What  other  materials  do  some  of  them  contain? 

5.  What  particular  office  do  the  living  organs  perform? 

6.  How  far  are  the  secretions  under  the  influence  of  chemical  affinity ? 


280  CONVERSATIONS  ON  CHEMISTRY. 

Mrs  B.  Exactly  so.  As  long  as  the  organized  being  lives  and  thrives, 
its  constituents  are  presented  to  each  other  in  such  a  way,  that  they  are  not 
susceptible  of  entering  into  other  combinations;  but  no  sooner  does  death 
take  place,  than  this  controlling  power  is  destroyed,  and  new  combinations 
are  produced. 

Emily.  But  why  should  death  destroy  the  combinations  which  have  been 
actually  formed;  the  principles  must  remain  in  the  same  proportions,  and 
consequently,  I  should  suppose,  in  the  same  order  of  attractions? 

Mm  B.  You  must  remember,  that  both  in  the  vegetable  and  animal 
kingdom,  it  is  by  the  principle  of  life  that  the  organs  are  enabled  to  act. 
When  deprived  of  that  agent,  or  stimulus,  their  power  ceases,  and  an  order 
of  attractions  succeeds,  similar  to  that  which  would  take  place  in  mineral, 
or  unorganized  matter(7). 

Emily.  It  is  this  new  order  of  attractions,  then,  that  destroys  the  organi- 
zation after  death;  for  if  the  same  combinations  still  continued  to  prevail, 
there  would  be  no  spontaneous  decay,  or  putrefaction,  but  the  being  would 
always  remain  in  the  form  possessed  by  it  when  it  died. 

Mrs  B.  And  that,  you  know,  is  never  the  case;  for  although  by  drying, 
or  other  processes,  it  may  be  partially  preserved  for  some  time  after 
death,  yet,  in  the  natural  course  of  events,  all  bodies  return  to  the  state  of 
simple  elements,  or  form  binary  combinations,  such  as  water,  carbonic 
acid,  carburetted  hydrogen,  &e.  In  this  we  see  an  admirable  dispensation  of 
Providence,  by  which  those  beings  that  have  ceased  to  live,  are  rendered  fit 
to  enrich  the  soil,  and  become  subservient  to  the  nourishment  of  others(8). 

Caroline.  You  have  exhibited  to  us  one  of  the  compounds  resulting 
from  the  exertion  of  those  affinities  which  produce  the  spontaneous  decom- 
position of  a  plant:  I  allude  to  the  carburetted  hydrogen,  collected  from  the 
vegetable  deposite  at  the  bottom  of  a  pond. 

Mrs  B.  The  prevailing  tendency  of  the  carbon  and  hydrogen  which 
every  plant  contains,  is  to  combine  with  so  much  oxygen  as  shall  convert 
them  into  carbonic  acid  and  water.  These  form  a  part  of  the  new  com- 
pounds evolved,  in  whatever  way  the  decomposition  of  a  vegetable  may  be 
effected.  But  in  most  vegetable  principles,  the  quantity  of  oxygen  con- 
tained is  insufficient  to  saturate  the  hydrogen  and  carbon,  and  these  latter 
principles,  therefore,  unite  together,  and  produce  the  carburetted  hy- 
drogen(9). 

Emily.  I  should  suppose  that  vegetable  substances  would  be  incombus- 
tible, if  the  oxygen  contained  in  them  were  sufficient  to  saturate  their  hy- 
drogen and  cai'bon;  as  in  this  case  they  would  have  no  tendency  to  combine 
with  the  oxygen  of  the  atmosphere(lO). 

Mrs  B.  Your  conclusion  is  undoubtedly  correct.  When  vegetables  are 
burnt  in  the  presence  of  oxygen,  water  and  carbonic  acid  are  almost  the 
exclusive  products;  but  when  heated  to  redness  in  close  vessels,  the  whole 
quantity  of  oxygen  which  they  contain  is,  in  many  cases,  employed  in  satu- 
rating a  small  part  only  of  their  hydrogen.  It  is  in  consequence  of  this  cir- 
cumstance that  certain  vegetable  products,  such  as  tar,  rosin,  and  bituminous 
coal,  are  sometimes  used  at  the  gas  works,  for  the  production  of  the  car- 
buretted hydrogen  with  which  some  of  our  large  cities  areilluminated(H). 

Emily.  The  odour  given  out  in  the  burning  of  animal  substances  differs 
very  much  from  that  of  vegetables;  this  difference  must  result  from  the  pre- 


7.  What  occurs  in  these  compounds  when  life  ceases? 

8.  What  useful  purpose  is  accomplished  by  their  disorganization? 

9.  What  is  the  prevailing  tendency   of  the  constituents  of  vegetables, 
and  what  the  actual  products  of  their  decomposition? 

10.  What  would  result  if  vegetables  contained  a  large  portion  of  oxygen? 

11.  What  is  the  result  when  they  are  heated  in  close  vessels? 


ON  VEGETABLE  CHEMISTRY.  281 

sence  of  nitrogen,  and  the  consequent  production  of  principles  not  evolved 
from  vegetables. 

Mrs  B.  Certainly:  this  additional  agent  gives  rise  to  new  affinities,  and~ 
of  course,  to  the  formation  of  new  products;  among  which  will  be  found 
both  ammonia  and  cyanogen.  There  are  a  few  vegetable  substances  which 
also  contain  nitrogen;  and  these  may,  in  general,  be  distinguished  by  their 
producing,  during  their  combustion,  an  odour  similar  to  that  given  out  by 
animal  matter. 

Caroline.  This  fourth  constituent  of  animal  malter  may  probably  ac- 
count for  its  greater  tendency  to  decomposition;  as  when  life  is  extinguished, 
the  affinities,  which  are  left  free  to  operate,  are  more  numerous  than  those 
which  produce  the  disorganization  of  vegetables(12). 

Mrs  B,  From  what  has  been  already  remarked,  you  may  perceive  that 
the  products  of  vegetation,  and  of  animalization,  are  characterized  by  the 
following  circumstances: — 1st,  by  being  composed  essentially  of  the  same 
elements; — 2d,  by  the  facility  with  which  they  undergo  spontaneous  decom- 
position;— 3d,  by  the  impracticability  of  forming  them  by  chemical  means; 
and  4th,  by  being  decomposed  at  a  red  heat(13). 

Emily  There  must,  undoubtedly,  be  a  considerable  difference  between 
the  products  of  decomposition  when  it  takes  place  spontaneously,  and  when 
it  is  effected  at  the  temperature  of  ignition. 

Mrs  B.  It  is  very  great;  but  even  at  the  temperature  of  ignition,  the  pre- 
sence or  the  absence  of  atmospheric  air  essentially  influences  the  result(l4). 
When  organized  substances  are  decomposed  at  a  red  heat  in  close  vessels, 
the  process  is  called  destructive  distillation.  In  this  case,  a  large  quantity 
of  charcoal  usually  remains  in  the  retort,  which,  had  atmospheric  air  been 
present,  would  have  been  converted  into  carbonic  acid.  The  volatile  pro- 
ducts, also,  which  escape,  are  not  products  of  combustion.  Tli  e  formation'of 
carburetted  hydrogen,  just  now  noticed,  may  serve  to  exemplify  this  fact. 

Caroline.  Certainly;  for  had  air  been  present,  the  carburetted  hydrogen 
would  have  combined  with  oxygen,  and  been  converted  into  carbonic  acid 
and  \vater(l5). 

Mrs  B.  Air  acts  an  important  part  also  in  the  slow  decomposition  of 
organic  matter;  but  its  influence  at  common  temperatures,  and  at  that  of  ig- 
nition, must  necessarily  vary  greatly.  Under  circumstances  so  different,  the 
principles  concerned  will  combine  in  proportions  very  dissimilar;  and  the  ex- 
tent to  which  the  decomposition  will  be  carried,  must  be  equally  varied(l6). 

Emily.  The  subject  of  organic  chemistry,  as  it  relates  both  to  vegeta- 
bles and  to  animals,  seems  very  naturally  to  divide  itself  into  two  parts.  I 
suppose  you  will  call  our  attention  to  these  separately. 

Mrs  B.  Yes;  and  we  shall  first  consider  what  is  denominated  VEGETA- 
BLE CHEMISTRY:  from  this  department  you  will  acquire  a  knowledge  of  the 
various  principles  obtained  by  the  decomposition  of  plants(17). 

Caroline.  Such  substances  must  be  capable  of  undergoing  two  kinds  of 
decomposition  very  different  from  each  other.  If,  for  example,  we  decom- 
pose a  vegetable  perfectly,  we  shall  obtain  from  it  nothing  but  oxygen,  hy- 
drogen, and  carbon;  and  every  kind  of  vegetable  would  yield  exactly  the 
same  materials.  But  vegetables  contain  oils,  and  acids,  and  sugar,  and  gum, 
and  juices  of  various  kinds;  the  decomposition  by  which  these  are  separated 


12.  What  is  the  effect  of  the  nitrogen  upon  those  substances  which  con- 
tain it? 

13.  What  are  the,  characteristics  of  the  products  of  organization? 

14.  What  is  said  of  their  decomposition  at  high  temperatures? 

15.  What  is  destructive  distillation,  and  what  is  said  respecting  it? 

16.  What  is  observed  respecting  the  influence  of  the  atmosphere? 

17.  What  is  intended  by  vegetable  chemistry? 

YO 
m 


282  CONVERSATIONS  ON  CHEMISTRY. 

from  each  other,  must  be  essentially  different  from  the  former  kind  of  de- 
composition; as  the  substances  obtained  are  themselves  still  capable  of  be- 
ing separated  into  others  more  simple. 

•Mrs  B.  Your  ideas  upon  this  point  are  judicious  and  correct.  A  ve- 
getable may  be  analyzed  for  the  purpose  of  discovering  what  are  the  differ- 
ent compounds  that  have  been  formed  in  it  during  the  period  of  its  growth, 
and  upon  the  chemical  character  of  which  its  particular  properties  depend; 
and  each  of  these  principles  may  in  its  turn  be  analyzed  in  order  to  ascer- 
tain the  proportionate  quantities  of  oxygen,  hydrogen,  and  carbon  of  which 
they  respectively  consist(18). 

Those  distinct  compounds  which  exist  ready  formed  in  a  plant,  are  call- 
ed its  PROXIMATE,  or  IMMEDIATE  PRINCIPLES.  Thus  sugar,  starch,  and 
gum  are  proximate  principles,  and  these  we  obtain  by  proximate  analysis. 
When  we  decompose  them,  to  ascertain  how  much  they  contain  of  each 
of  the  simple  bodies,  the  operation  is  called  ultimate  analyitis(l$).  This, 
however,  is  a  process  of  great  delicacy,  as  in  attempting  to  obtain  the 
proximate  principles,  we  are  in  danger  of  decomposing  them  by  the  agents 
we  employ;  and  in  reducing  them  into  their  ultimate  principles,  the  pre- 
sence of  air  or  of  moisture  may  supply  us  with  a  portion  of  oxygen  or  of 
hydrogen,  and  thus  lead  us  to  a  wrong  estimate  of  the  quantity  of  these 
substances  contained  in  the  article  under  examination(20). 

Emily.  The  sap  of  plants,  is,  I  suppose,  one  of  their  proximate  princi- 
ples, and  as  this  can  be  obtained  without  using  heat,  or  any  other  agent  cal- 
culated to  decompose  it,  there  can  be  but  little  difficulty  in  ascertaining  its 
properties. 

J\frs  B.  The  sap  contained  in  vegetables  is  not  to  be  considered  as  a 
single  proximate  principle,  but  as  a  very  complex  mixture  of  several  of  them 
in  solution,  together  with  the  ingredients  which  the  roots  have  sucked  up 
from  the  soil,  and  from  which  the  variods  organs  of  the  plant  secrete  f\nd 
appropriate  those  materials  which  are  necessary  to  its  nourishment,  and  to 
the  formation  of  the  stem,  the  leaves,  the  fruit,  and  all  the  other  parts(21). 

Caroline.  In  the  ultimate  analysis  of  plants  I  suppose  that  the  sour  jui- 
ces of  fruits,  and  other  acid  parts,  are  found  to  contain  more  oxygen  than 
those  which  are  either  sweet,  or  bitter;  as,  from  the  composition  of  plants, 
oxygen  must  necessarily  be  their  acidifying  principle. 

Jtfrs  B.  Such  is  the  fact;  and  those  parts  which  are  the  most  eminently 
combustible,  as  the  resins  and  oils,  for  example,  abound  more  in  hydrogen 
and  carbon.  We  are  indebted  to  those  distinguished  French  chemists  Gay- 
Lussac  and  Thenard,  for  some  valuable  researches  upon  this  subject.  From 
the  ultimate  analysis  of  a  great  number  of  vegetable  compounds,  these  phi- 
losophers were  led  to  divide  the  proximate  principles  of  plants  into  three 
classes,  depending  upon  the  proportionate  quantity  of  oxygen  and  hydrogen 
contained  in  each(22).  Those  ingredients  may  exist  in  such  compounds,  in 
the  same  proportions  in  which  they  do  in  water,  or  there  may  be  an  excess 
of  either  of  them.  Thejirst  class  embraces  those  substances  in  which  there 
is  more  than  a  sufficient  quantity  of  oxygen  to  convert  all  the  hydrogen  into 
water:  to  this  belong  the  vegetable  acids.  The  second  class  contains  those  in 
which  there  is  more  hydrogen  than  is  sufficient  to  combine  with  the  oxygen 
in  the  production  of  water:  these  principles  are  oily,  resinous,  or  alcoholic. 
In  the  third  class,  the  oxygen  and  hydrogen  are  in  those  exact  proportions 


L8.   To  what  two  kinds  of  analysis  may  such  substances  be  subjected? 

19.  What  are  called  the  proximate,  and  what  the  ultimate  principles? 

20.  Why  is  the  analysis  of  plants  an  operation  of  great  delicacy? 

21.  Why  is  not  the  sap  accounted  a  proximate  principle? 

22.  Upon  what  is  the  classification  of  proximate  principles  founded? 


ON  VEGETABLE  PRINCIPLES.  283 

which  form  water:  these  are  neither  acid  nor  x*esinous.  Sugar,  gum,  starch, 
with  many  others,  are  of  this  class(23). 

Caroline.  That  is  a  very  satisfactory  arrangement,  as  it  gives  to  us  some 
idea  of  the  composition  of  a  body  from  its  sensible  properties.  I  should 
like  to  have  a  list  of  these  acids  and  other  compound  principles,  that  I 
might  take  a  glance  at  the  ground  over  which  we  are  to  travel  in  search  of 
these  animal  and  vegetable  remains. 

Mrs  B.  Such  a  list  would  be  more  formidable  than  you  anticipate,  and 
would  contain  the  names  of  many  substances  for  the  examination  of  which 
we  have  neither  time  nor  opportunity.  To  gratify  you,  however,  I  will  give 
you  a  catalogue  of  some  of  these  principles,  confining  it  to  the  vegetable 
kingdom  only.  Here  it  is. 

Vegetable  Jidda. 

Acetic,  Citric,  Gallic,  Hydrocyanic, 

Oxalic,  Malic,  Succinic,  Kinic, 

Tartaric,  Benzoic,  Moroxylic,  Meconic(24). 

Substances  -which  are  chief  y  Alkaline. 

Morphia,  Strychnia,  Emetin,  Solania, 

Cinchonia,  Brucia,  Picrotoxia,  Delphia(25), 

Quinia,  Veratria. 

Substances  of  the  Second  Class. 

Fixed  Oils  of  various  kinds,  Gum  Resins,  of  several  kinds, 

Volatile  oils,  a  large  class,  Caoutchouc, 

Camphor,  Wax, 

Resins,  numerous,  Bituminous  substances(26). 

Substances  chiefly  of  the  Third  Class,  but  some  of -which  are  not  determined. 
Sugar,  Colouring  Gliadine,  Fungin, 

Fecula,  or  Starch,     matter,  Zymome,  Suberin, 

Gum,  Tannin,  Vegetable  albu-      Ulmin,&c.(27). 

Lignin,  Gluten,  men, 

If  this  list  is  too  brief,  I  have  the  means  of  adding  to  it  the  names  of 
a  great  many  other  substances. 

Caroline.  Indeed,  madam,  I  am  more  than  satisfied  with  its  extent,  and 
have  no  desire  to  learn  the  history  of  all  those  bodies  which  your  list  pre- 
sents to  us,  as  I  presume  that  some  of  them  must  be  quite  insignificant  per- 
sonages. 

Emily.  Do  all  the  acids  which  you  have  named  exist  ready  formed  in 
plants,  or  are  not  some  of  them,  like  carbonic  acid,  the  result  of  the  decom- 
position of  vegetable  matter,  and  the  union  of  its  constituents  in  new  forms;* 

Mrs  B.  All  those  which  I  have  enumerated  exist  in  plants  either  in  a  free 
state,  or  combined  with  salifiable  bases.  A  few  of  them  also  may  be  artifici- 
ally produced  by  the  chemist;  and  in  some  instances  they  may  be  converted 
into  each  other,  and  especially  into  acetic  acid,  or  vinegar,  by  processes  which 
abstract  a  portion  of  their  oxygen(28).  With  the  exception  of  the  oxalic 
acid,  they  all  consist  of  oxygen,  carbon,  and  hydrogen,  combined  in  different 


23.  How  is  each  of  the  three  classes  distinguished? 

24.  Name  such  of  the  vegetable  acids  as  you  may  recollect. 

25.  Do  the  same  with  the  alkaline  principles. 

26.  What  substances  compose  a  part  of  the  second  class? 

27.  What  of  the  third  class? 

28.  What  is  observed  respecting  the  vegetable  acids? 


284  CONVERSATIONS  ON  CHEMISTRY. 

proportions.  They  are  therefore  considered  as  having  a  double  base,  carbon 
and  hydrogen,  acidified  by  means  of  oxygen(29). 

We  must  content  ourselves  with  a  short  notice  of  each  of  these  acids.  The 
first  on  our  list,*  how  ever,  we  shall  defer  until  a  future  occasion,  for  although 
it  is  found,  in  sparing  quantities,  in  some  living  plants,  it  is  usually  a  pro- 
duct of  fermentation. 

Emily.  The  OXALIC  ACID,  you  have  intimated,  differs  in  its  composition 
from  the  other  vegetable  acids:  this  difference,  of  course,  must  be  in  its 
base? 

•Mrs  B.  Whilst  all  the  others  contain  hydrogen,  oxalic  acid  consists, 
like  the  carbonic,  of  oxygen  and  carbon  only;  but,  .unlike  carbonic  acid, 
it  exists  in  the  solid  form,  crystallizing  in  four  sided  prisms.  It  is  a  viru- 
lent poison,  and  many  lives  have  been  destroyed  by  its  crystals  being  mis- 
taken for  those  of  Epsom  salts.  The  sour  taste  of  common  sorrel,  (rumetf 
acetosa),  and  of  wood  sorrel,  (oxalis  acetosella),  is  derived  from  the 
presence  of  oxalic  acid;  not  alone,  however,  but  combined  with  a  portion 
of  potassa,  in  the  form  of  abinoxalate  ofpotassa.  This,  when  crystallized, 
is  sold  under  the  name  of  essential  salt  of  lemons,  and  is  used  for  the  pur- 
pose of  taking  iron  moulds  out  of  linen.  It  effects  this  by  forming  a  soluble 
salt  with  the  oxide  of  iron(SO). 

Emily.  The  TARTAHIC  ACID,  the  second  on  your  list,  is,  I  suppose,  the 
same  that  we  commonly  call  cream  of  tartar,  and  which  forms  so  pleas- 
ant an  acid  drink. 

Mrs  B.  Tartaric  acid  exists  in  vegetables,  combined,  like  the  oxalic, 
with  an  alkaline  base,  but  not  in  such  a  proportion  as  to  form  a  neutral  salt. 
Common  cream  of  tartar  is  a  bitartrate  of  potassa.  It  is  contained  in  the 
juice  of  the  grape;  and  is  found  forming  an  incrustation  on  the  inside 
of  vessels  in  which  wine  has  fermented(Sl). 

Caroline.  This  acid  you  mentioned,  I  believe,  as  being  contained  in 
Rochelle  salt,  which  you  called  a  double  salt. 

Mrs  B.  Yes;  if  the  bitartrate  ofpotassa  is  dissolved,  and  soda  added  to 
the  solution  until  the  excess  of  acid  is  neutralized,  on  evaporating  the  wa- 
ter, beautiful  crystals  of  the  tartrate  of  potash  and  soda  (Rochelle  salt) 
will  be  obtained.  Tartar  emetic  is  also  a  double  salt,  containing  potassa 
and  oxide  of  antimony  combined  with  tartaric  acid.  Its  proper  name,  there- 
fore, is  tartrate  of  antimony  and  potassa(32}. 

Caroline.  That  is  a  salt  for  which  I  have  no  affinity  whatever,  and 
which  I  am  quite  willing  to  place  among  the  incompatibles. 

Mrs  B.  CITRIC  ACID  is  found  in  many  fruits,  but  principally  in  lemons 
and  limes.  It  is  frequently  preserved  in  the  crystalline  form,  and  used 
instead  of  the  fresh  fruit,  in  making  punch  and  lemonade.  Its  salts  are 
called  citrates(33). 

MALIC  ACID  exists  in  apples,  and  in  most  of  the  acidulous  fruits,  accom- 
panied by  other  acids,  and  by  saccharine  matter. 

BETV  zoic  ACID  is  obtained  from  a  substance  called  benzoin.  Its  taste  is  ra- 
ther aromatic  and  pleasant,  on  which  account  it  is  used  in  some  medicinal 
preparations(34).  The  gallic  acid  is  the  only  one  remaining  on  our  list, 
to  which  I  shall  deem  it  necessary  to  require  your  further  attention. 

GALLIC  ACID  is  contained  in  gall  nuts,  and  also  in  the  bark  of  oak  and  va- 
rious trees.  It  is  always  combined  with  other  principles,  but  especially 


29.  What  are  their  general  constituents,  and  what  exception  is  there? 

30.  How  is  oxalic  acid  found,  and  what  are  its  properties? 

31.  Whence  is  tartaric  acid  obtained,  and  with  what  combined? 

32.  What  are  Rochelle  salt  and  tartar  emetic? 
S3.  What  is  said  of  citric  acid? 

34.   In  what  are  malic  and  benzole  acids  contained? 


ON  VEGETABLE  ACIDS  AND  ALKALIES.  285 

with  tannin.  When  these  substances  are  infused  in  water,  the  gallic  acid 
is  dissolved(35).  In  this  phial  I  have  a  solution  of  gall  nuts,  which,  although 
of  a  brownish  colour,  is  perfectly  transparent;  and  in  this  other  phial  l'  have 
a  solution  of  sulphate  of  iron.  Observe  the  effect  when  I  mix  together  a 
small  portion  of  each  of  them. 

Emily.  They  have  instantaneously  become  as  black  as  ink,  and  are  quite 
opake ! 

Mrs  B.  They  have  actually  formed  ink.  The  most  distinguishing  pro- 
perty of  gallic  acid  is,  that  when  combined  with  the  salts  of  iron,  it  produ- 
ces an  intensely  blue  colour,  approaching  to  black(36).  This  acid  can  he 
obtained  in  the  crystalline  state:  its  taste  is  both  sour  and  astringent.  With 
the  exception  of  that  formed  by  its  combination  with  iron,  its  salts  are  un- 
important. 

Emily.  Are  not  the  gall  nuts  somewhat  similar  to  the  oak  apples  which 
we  frequently  see  in  this  country? 

Mrs  JB.  They  are  both  produced  in  the  same  way;  that  is  by  the  punc- 
ture which  an  insect  makes  for  the  purpose  of  depositing  its  egg.  The  oak 
apples,  however,  are  soft  and  spongy,  whilst  gall  nuts  are  solid  and  hard. 
The  best  kind  come  from  the  countries  on  the  Levant,  and  are  called  Aleppo 
galls.  They  are  extensively  used,  not  only  in  the  making  of  ink,  but  also 
for  the  purpose  of  dyeing  a  black  colour(37). 

We  shall  now  notice,  in  a  brief  way,  a  very  important  class  of  compounds 
which  the  chemist  has  extracted  from  various  vegetable  substances,  and  in  so 
doing  has  furnished  the  physician  with  the  active  principles  of  many  plants, 
divested  of  the  inert,  and,  in  some  instances,  the  injurious  substances  with 
which  they  are  mixed,  or  combined,  in  the  plant:  I  allude  to  the  VEGETA- 
BLE ALKALIES. 

Caroline.  These  are  very  different  substances  from  potash,  which  you 
informed  us  was  at  one  time  called  the  vegetable  alkali,  as  they  are  actually 
vegetable  principles.  They  must  consist  of  the  very  same  ingredients  as 
the  acids  which  we  have  just  been  considering(38). 

Jlfrs  £.  It  appears  that  the  vegetable  alkalies  contain  nitrogen,  in  addi- 
tion to  the  three  principles  found  in  all  vegetables.  Two  or  three  examples 
of  these  alkalies  will  suffice  to  give  you  an  idea  of  their  nature  and  use. 

MORPHIA  is  found  to  be  the  narcotic  principle  ot  opium;  but  in  that  drug, 
there  are  various  other  substances,  one  of  which  is  called  narcotine;  and  it  is 
from  the  presence  of  this  article  that  proceed  the  extremely  unpleasant 
effects  produced  upon  some  persons  by  the  use  of  opium.  When  the  mor- 
pMa  is  procured  in  a  separate  state,  the  soothing  effects  of  opium  are  pro- 
duced without  that  feverish  excitement  which  so  often  results  from  laudan- 
um and  opium,  as  usually  administered(39). 

CitfCHOifiA,  and  QJJINIA,  or  Q.UIKINE,  are  alkaline  principles,  and  both  con- 
tained in  Peruvian  bark.  They  are  also  bitter  principles,  and  although  evi- 
dently different  from  each  other,  are  analogous  in  their  medicinal  proper- 
ties. They  both  form  salts  with  nearly  all  the  acids.  That  which  is  most 
employed  is  the  sulphate  of  quinia.  In  this  substance  the  active  principle 
of  the  bark  is  so  concentrated,  that  two  or  three  grains  of  it  have  proved  as 
effectual  in  curing  intermittent  fever,  as  many  ounces  of  the  solid  bark(40). 

We  will  now  pass  on  to  the  second  class  of  the  vegetable  proximate  prin- 
ciples. 


35.  Whence  is  gallic  acid  procured,  and  with  what  is  it  combined? 

36.  What  is  produced  by  its  mixture  with  sulphate  of  iron? 

37.  How  are  gall  nuts  produced,  and  in  what  countries? 

38.  What  is  said  respecting  the  vegetable  alkaline  principles? 

39.  What  observations  are  made  respecting  morphia  and  narcotine? 

40.  What  in  relation  to  cinchonia  and  quinia? 


286  CONVERSATIONS  ON  CHEMISTRY.1 

Emily.  That  is  to  the  oily,  resinous,  and  alcoholic  substances,  in  which 
the  hydrogen,  when  compared  with  the  oxygen,  is  in  excess. 

Mrs  B.  OILS  are  divided  into  fixed,  and  volatile.  FIXED  OILS  are  so 
called  because  they  require  a  very  high  degree  of  heat  to  convert  them  into 
vapour;  whilst  the  volatile  oils  evaporate  at  the  common  temperature  of  the 
atmosphere.  A  drop  of  fixed  oil  will  produce  a  permanent  spot  of  grease 
upon  paper;  whilst  a  drop  of  volatile  oil  will  rapidly  evaporate,  especially 
if  the  paper  he  held  before  the  fire(4l). 

Caroline.  Nuts  sometimes  contain  a  large  quantity  of  oil;  and  I  believe 
that  it  is  from  the  seeds  of  plants  that  the  oils  are  always  obtained. 

Mrs  B.  Olive  oil  is  extracted  from  the  pulp  which  surrounds  the  stone; 
but  the  fixed  oils  are  usually  contained  in  the  seeds  only.  They  are  gene- 
rally obtained  by  bruising  the  seeds,  and  then  putting  them  under  a  press 
in  strong  bags  made  of  hemp  or  horse  hair.  Linseed  oil  is  thus  pressed 
from  the  seed  of  flax.  Walnuts,  almonds,  and  poppy,  cotton,  sun-flower, 
rape,  and  many  other  seeds,  supply  considerable  portions  of  oil(42). 

Emily.  There  is  one  very  striking  difference  between  these  fixed  oils; 
the  linseed  and  nut  oils  which  1  use  in  my  painting,  dry  and  become  hard, 
which  would  never  be  the  case  with  olive  oil. 

Mrs  B.  These  are  called  drying  oils,  and  they  appear  to  possess  this 
property  in  consequence  of  their  affinity  for  oxygen,  of  which  they  absorb  a 
large  quantity,  and  thus  become  converted  into  hard  substances,  resembling 
the  resins(43). 

Caroline.  If  they  absorb  a  large  quantity  of  oxygen,  I  wonder  they  do 
not  heat,  and  take  fire,  as  this  would  seem  to  be  a  natural  result. 

Mrs  B.  Recollect  that  to  produce  combustion  the  absorption  must  be 
rapid  as  well  as  great.  It  is  a  fact,  however,  that  combustion  has  frequently 
taken  place  from  this  cause.  If  hemp,  cotton,  or  similar  materials  be 
moistened  with  drying  oil,  and  laid  in  a  heap,  it  will,  in  the  course  of  a 
few  hours,  heat  and  take  fire.  Many  destructive  conflagrations  have  re- 
sulted from  spontaneous  combustions  of  this  kind.  When  a  single  article 
is  oiled,  and  exposed  to  the  cooling  influence  of  the  atmosphere,  the  heat 
will  be  carried  off"  as  fast  as  it  is  generated;  but  where  there  is  a  mass  of  the 
material,  the  heat  is  retained  and  accumulated(44). 

Emily.  From  your  remark  that  the  fixed  oils  are  usually  contained  in 
the  seeds  only,  and  are  procured  by  pressure,  I  infer  that  such  is  not  the 
fact  as  regards  the  volatile  oils. 

Mrs  B.  The  VOLATILE,  or  ESSENTIAL  OILS,  form  the  basis  of  all  the 
vegetable  perfumes. '  Essential  oil  is  contained,  more  or  less,  in  every  part 
of  an  odoriferous  plant,  excepting  the  seeds.  Many  flowers  contain  it  in 
considerable  quantities. 

Emily.  It  is  then  from  essential  oil,  I  suppose,  that  their  odour  pro- 
ceeds? 

Mrs  B.  Yes;  and  this  oil  is  frequently  obtained  from  flowers.  In  a 
few  instances,  as  from  the  rind  of  lemons  and  oranges,  essential  oil  may  be 
obtained  by  simple  pressure:  this,  however,  can  very  seldom  be  done(45). 

Caroline.  Is  it  not  very  plentiful  in  the  leaves  of  mint,  and  of  thyme, 
and  all  the  sweet  smeJling  herbs? 

Mrs  B.  Yes,  remarkably  so;  and  in  geranium  leaves  also,  which  have 
a  much  more  powerful  odour  than  the  flowers. 

The  perfume  of  sandal  fans  is  an  instance  of  its  existence  in  wood.     In 


41.  How  we  fixed  and  volatile  oils  distinguished? 

42.  In  what  way  and  from  what  parts  are  the  fixed  oils  procured? 

43.  By  what  are  the  drying  oils  distinguished? 

44.  How  do  they  occasionally  produce  spontaneous  combustion? 

45.  In  what  parts  of  a  plant  are  the  essential  oils  found? 


ON  ESSENTIAL  OILS  AND  RESINS.  287 

short,  all  vegetable  odours,  or  perfumes,  are  produced  by  the  evaporation  of 
particles  of  these  volatile  oils(46).  The  usual  mode  of  obtaining  essential 
oils  is  by  distillation.  The  aromatic  plant  is  put  into  a  still,  along  with 
water,  without  which  the  vegetable  would  be  burnt.  The  essential  oil  and 
•water  pass  over,  and  are  condensed  in  a  receiver.  The  oil,  being  inso- 
luble in  the  water,  floats  upon  its  surface,  or  sinks  to  the  bottom,  according 
to  its  specific  gravity(47). 

Emily.  What  is  the  difference  between  what  are  called  essences  and 
the  volatile  oils. 

-  Mrs  JB.  The  volatile  oils  are  soluble  in  alcohol,  and  the  essences  are 
solutions  of  this  kind:  thus  essence  of  peppermint  consists  of  the  essential 
oil  of  peppermint  and  alcohol.  Essences  are  formed  by  using  ardent  spirit, 
or  alcohol,  instead  of  water,  in  the  distillation  of  the  aromatic  plants(48). 

The  essential  oils  evaporate  but  slowly  at  common  temperatures;  and, 
like  the  drying  oils,  when  exposed  to  the  atmosphere,  they  absorb  oxygen, 
thicken,  and  at  length  acquire  a  consistence  resembling  the  resins(49). 

The  cheapest  and  most  useful  of  the  essential  oils,  is  the  oil,  or  spirits,  of 
turpentine,  which*is  procured  by  distilling  the  turpentine  which  oozes  from 
the  pine  tree.  Common  rosin  is  the  substance  which  remains  in  the  still, 
after  the  volatile  oil  is  driven  over(50). 

Caroline.  Pray  does  not  the  powerful  smell  of  camphor  proceed  from  a 
volatile  oil? 

Mrs  B.  CAMPHOR,  although  closely  allied  to  the  volatile  oils  in  many 
respects,  seems  in  others  to  stand  alone.  It  is  obtained  from  a  tree  in  Japan, 
called  the  laurus  camphora.  Like  the  essential  oils  it  is  diffused  through- 
out the  plant,  and  is  separated  from  the  trunk,  root,  and  branches,  by  sub" 
limation.  Camphor  is  found  in  small  quantities  in  various  other  plants. 

Camphor  is  soluble  in  the  essential  and  fixed  oils,  and  in  alcohol,  but  is 
insoluble  in  water.  By  its  aid  copal,  one  of  the  resins,  may  be  rendered 
soluble  in  alcohol,  and  converted  into  a  varnish(Sl). 

Emily.  The  different  vai'nishes  are,  I  know,  made  from  the  resins,  and 
as  I  sometimes  use  them,  I  feel  interested  in  learning  something  further 
respecting  their  composition. 

Mrs  B.  The  RESINS  are  the  inspissated  juices  of  plants,  which,  although 
they  resemble  the  glims  in  appearance,  differ  from  them  essentially  in  their 
properties.  The  different  kinds  of  gum  are  soluble  in  water,  whilst  in  this 
fluid  the  resins  are  completely  insoluble,  their  proper  solvents  being  the 
fixed  and  volatile  oils,  alcohol  and  ether.  The  resins  are  also  dissolved  by 
means  of  the  fixed  alkalies.  They  undergo  fusion  by  heat,  are  extremely 
combustible,  affording  a  brilliant  light,  and,  like  the  oils,  produce  in  their 
combustion  carbonic  acid  and  water(52). 

The  principal  resins  are  common  rosin,  copal,  lac,  sandarach,  maslich, 
and  elemi.  All  these  when  dissolved  are  used  in  varnishes(53). 

Emily.  But  I  believe  they  are  not  all  soluble  in  the  same  fluids,  as  the 
spirit  and  oil  varnishes  usually  contain  different  resins. 

Mrs  B.  They  are,  in  some  instances,  and  under  proper  management, 
soluble  in  the  essential  and  fixed  oils,  and  also  in  alcohol;  but,  in  general, 


46.  What  particular  plants  are  named  as  abounding  in  it? 

47.  How  are  the  essential  oils  usually  procured? 

48.  In  what  do  the  essences  differ  from  the  essential  oils? 

49.  What  change  does  the  atmosphere  produce  in  them? 

50.  What  is  spirits  of  turpentine,  and  what  rosin? 

51.  What  is  camphor,  and  what  is  said  respecting  it? 

52.  What  are  the  resins,  and  what  are  their  properties? 

53.  Name  some  of  the  principal  resins. 


288  CONVERSATIONS  ON  CHEMISTRY. 

they  have  their  appropriate  solvents,  and  become  the  basis  of  oil  or  of  spirit 
varnishes,  according  to  the  difference  in  their  natures(54). 

Caroline.  Is  not  amber  a  resin?  it  has  that  appearance,  and  I  have  heard 
of  amber  varnish. 

•Mrs  B.  AMBER  is  a  peculiar  resinous  substance,  undoubtedly  of  vege- 
table origin;  but  it  is  sometimes  dug  out  of  the  earth,  and  at  others  collected 
in  cei'tain  places  on  the  sea  shore.  Its  precise  origin  is  unknown,  but  it  is 
certainly  a  vegetable  product,  as  it  frequently  includes  insects,  and  small 
pieces  of  plants  within  its  substance(55). 

There  is  a  mixture  of  essential  oil,  of  resin,  gum,  and  other  matter,  ob- 
tained in  a  concrete  state,  from  different  plants,   and  called  GUM-RESIXS. 
viloes,  gamboge^  and  several  other  useful  compounds  belong  to  this  class(56). 
Emily.     Does  not  gum  elastic  also  belong  to  the  same  family  ?  it  is  a  very 
inflammable  substance,  as  I  have  frequently  observed. 

Mrs  B.  CAOUTCHOUC,  or  gum  elastic,  when  first  procured  from  the 
plants  which  contain  it,  is  a  white,  milky,  glutinous  fluid;  it  acquires  con- 
sistence and  blackens  in  drying. 

Caroline.  I  am  surprised  to  hear  that  gum  elastic  was  ever  white  or  ever 
fluid.  From  what  vegetable  is  it  procured? 

Mrs  B.  There  are  two  or  three  different  species  of  trees  in  the  East 
Indies  and  South  America,  from  which  it  is  obtained  by  making  incisions  in 
their  stems.  The  juice  is  collected  as  it  trickles  from  these  incisions,  and 
moulds  of  clay,  in  the  form  intended  to  be  given  to  the  bottles  of  gum  elas- 
tic, are  dipped  into  it.  A  layer  of  this  juice  adheres  to  the  clay,  and  dries 
on  it;  and  by  repeating  this  operation,  several  layers  are  successively  added 
until  the  bottle  is  of  sufficient  thickness.  It  is  then  beaten  to  break  down 
the  clay,  which  is  easily  shaken  out.  Shoes  and  boots  are  also  made  of  it  by 
a  similar  process.  They  are  extremely  pleasant  and  serviceable,  both  from 
their  elasticity,  and  their  being  perfectly  water  proof(57). 

We  will  next  say  a  few  words  respecting  the  ivax  which  is  collected  by 
that  industrious  insect  the  bee. 

Emily.  I  recollect  that  Huber,  in  his  most  interesting  work  upon  bees, 
considers  wax  as  an  animal,  rather  than  a  vegetable,  product;  as  he  found 
that  bees  made  combs  of  wax  even  when  they  were  fed  exclusively  upon 
sugar. 

Mrs  B.  WAX  partakes  of  the  nature  of  a  concrete  fixed  oil,  and  appears 
to  be  both  of  vegetable  and  of  animal  origin.  The  fact  you  mention  seems 
clearly  to  prove  the  latter,  whilst  the  former  is  evident  from  its  being  con- 
tained in  the  pollen  of  flowers,  and  from  its  forming  a  coating  to  the  plum, 
and  to  the  leaves  of  many  plants;  and  more  especially  from  the  quantity  ob- 
tained under  the  name  of  myrtle  -wax,  from  the  berries  of  the  myrica  ceri- 
fera.  There  appears,  however,  to  be  some  difference  in  the  composition  of 
that  procured  directly  from  plants  and  that  furnished  by  the  bee. 

Wax  is  frequently  made  into  candles,  as  it  affords  a  purer  light  than  most 
other  substances.  Before  being  used  for  this,  and  several  other  purposes, 
it  is  in  general  bleached,  and  rendered  perfectly  white(58). 

Caroline.     In  your  list  of  vegetable  principles  of  the  second  class,  yon. 
have  inserted   bituminous  substances.     I  had  always  supposed  that  these 
were  dug  out  of  the  earth,  and  properly  belonged  to  the  mineral  kingdom. 
Mrs  B.     They  may,  perhaps  with  equal  propriety,  be  classed  as  belong- 
ing either  to  the  mineral  or  the  vegetable  kingdom;  for  although  the  bitumens 


54.  What  is  said  respecting  their  solution,  and  of  varnishes? 

55.  Whataretheorigin,  sources,  and  properties  of  amber? 

56.  What  is  the  nature  of  the  gum-resins? 

57.  Give  the  history  of  caoutchouc,  or  gum  elastic. 

58.  Do  the  same  in  relation  to  ivax. 


ON  BITUMINOUS  SUBSTANCES.  289 

are  found  in  the  earth,  they  are  undoubtedly  of  vegetable  origin.      They 
may   be  conveniently  arranged  under  the   heads   of    Bitumen   and    Pit 


The  name  BITUMEN  includes  naphtha,  which  has  been,  already  noticed, 
(p.  164)  petroleum,  and  mineral  tar.  They  are  very  viscid  fluids,  bearing  a 
strong  resemblance  to  each  other.  They  are  found  in  many  coal  districts, 
and,  by  exposure  to  the  air,  become  solid,  and  appear  much  like  common 
pitch.  The  bitumens  are  distinguished  by  their  inflammability(60). 

Emily.  Common  pitch  and  tar,  however,  are  not  mineral  substances;  as 
they  are  brought  from  the  pine  districts,  where  turpentine  is  prepared. 

Mrs  B.  Turpentine  exudes  from  the  growing  pine  tree;  but  tar  is  ex- 
tracted from  the  wood  by  means  of  heat,  and  consists  of  the  turpentine  par- 
tially decomposed,  and  mixed  with  other  vegetable  products.  When  the 
more  fluid  parts  are  evaporated  by  boiling,  the  tar  is  converted  into  pitch. 
The  difference  between  them  and  mineral  tar,  and  mineral  pitch,  is  not 
greater  than  might  be  expected  in  substances  having  the  same  origin,  but 
obtained  by  different  processes(Gl).  Jlsphaltum,  sometimes  called  Jew's 
pitch,  is  a  much  purer  bitumen  than  common  pitch.  It  is  found  on  the  banks 
of  the  Dead  Sea,  and  in  the  islands  ofBarbadoes  and  Trinidad,  forming 
large  beds  in  the  earth.  Dissolved  in  spirits  of  turpentine,  it  forms  a  dark 
coloured  varnish  much  used  for  some  purposes(62).  Articles  very  similar 
to  most  of  these  bitumens  may  be  extracted  from  pit  coal, 

Caroline.  It  is  no  easy  thing  to  believe  that  the  vast  beds  of  pit  coal  ex- 
isting in  various  parts  of  the  world,  and  buried  far  below  the  surface  of  the 
ground,  have  all  originated  from  vegetable  materials.  Wood  and  coal  bear 
but  little  resemblance  to  each  other,  excepting  in  the  fact  that  they  are  both 
combustible. 

Mrs  B.  In  a  comparison  of  this  kind  the  fact  of  a  similarity  in  composi- 
tion is  a  point  of  much  greater  weight  than  that  of  mere  combustibility.  <jput 
we  have  still  strongei*  evidence,  in  the  fact  that  specimens  are  sometimes 
found  in  coal  mines,  one  part  of  which  exhibits  the  organic  structure  of  the 
wood,  in  the  form  of  charcoal,  whilst  another  part  is  completely  converted 
into  pit  coal.  The  slate  which  usually  covers  the  beds  of  pit  coal,  abounds 
also  in  petrified  vegetable  remains.  This  however  is  a  point  which  it  is  not 
our  present  business  to  discuss(63). 

Emily.  In  pit  coal  itself  there  must  be  a  great  difference  of  composi- 
ti6n.  The  anthracite  of  Pennsylvania,  and  the  coal  brought  from  Virginia 
or  from  England,  burn  as  differently  as  do  charcoal  and  yellow  pine 
wood. 

%  Mrs  B.  The  difference  between  the  two  is  precisely  that  which  exists  be- 
tween the  articles  that  you  have  named.  One  of  them  contains  a  bituminous, 
or  resinous  substance;  the  other  does  not(64).  The  best  anthracite  is  nearly 
pure  carbon;  and  if  we  take  the  bituminous  coal,  and  treat  it  as  we  do  pine 
wood  when  we  convert  it  into  charcoal,  the  bitumen  will  be  volatilized  by  the 
heat,  mineral  tar  and  pitch  may  be  collected  during  the  process,  and  a  spe- 
cies of  charcoal  will  then  remain,  which  is  called  COKE.  Excepting  in  its 
being  very  porous,  this  substance  is  very  similar  to  anthracite,  and  it  is  pre- 


59.  What,  observations  are  made  respecting  the  bitumens? 

60.  What  are  the  names  of  the  jtfm'd  bitumens? 

61.  What  is  said  respecting  turpentine,  tar,  and  pitch? 

62.  Where  is  asphaltum  found,  and  what  is  it  used  for? 

63.  What  circumstances  prove  the  vegetable  origin  of  pit  coal? 

64.  In  what  consists  the  difference  between  anthracite  and  the  common 
pit  coal? 

z 


290  CONVERSATIONS  ON  CHEMISTRY. 

pared  and  used  in  great  quantities  in  the  English  iron  manufactories  as  a 
substitute  for  charcoal(65). 

What  I  have  further  to  say  upon  vegetable  chemistry  will  afford  us  full 
occupation  during  our  next  meeting. 


CONVERSATION  XXIX. 

ON  VEGETABLE  CHEMISTRY— CONTINUED. 

Vegetable  Principles  of  the  Third  Class.  Sugar  and  its  Manufacture. 
Molasses,  Loaf-sugar,  Sugar-candy,  and  Barley  Sugar.  Honey,  Sugar 
of  Grapes,  and  Manna.  Gum  or  Mucilage.  Distinction  bet-ween  Gums 
and  Resins.  Fecula  or  Starch,  Jirroiv  Root,  Tapioca,  and  Sago.  Fe- 
cula  converted  into  Sugar  by  Sulphuric  JLcid,  by  Fermentation,  and  by 
Germination.  Malting.  Gluten.  Tannin.  Lignin  or  Woody  Fibre. 
Colouring  Matter,  Lakes,  and  Dyeing.  Adjective  and  Substantive  Co- 
lours, and  Mordants.  Fermentation.  Saccharine.  Vinous.  Use  of 
Yeast.  Nature  and  Combustion  of  Jllcohol.  Ethers.  Sulphuric  Ether, 
^phlogistic  Lamp.  Acetous  Fermentation,  Jlcetic  Acid,  Vinegar,  and 
Pyroligneous  Acid.  Products  of  the  Putrefactive  Fermentation. 

Mrs  B.  Our  first  business  to-day  will  be  to  examine  a  few  of  those  veg- 
etable principles  which  constitute  the  third  class;  that  in  which  the  oxygen 
and  hydrogen  are  to  each  other  in  the  proportion,  by  weight,  of  eight  to  one, 
or,  in  other  words,  in  the  exact  proportions  for  forming  water(l).  The  first 
of  tiiis  class  of  substances  which  will  claim  your  attention  is  sugar. 

Caroline.  Should  all  the  members  of  the  class  possess  qualities  equally 
agreeable,  we  shall  find  ourselves  in  very  pleasant  company. 

Emily.  SUGAR,  I  know,  is  contained  in  a  great  number  of  vegetables;  I 
have  seen  some  beautifully  white,  which  was  made  in  France  from  the  juice 
of  beets;  and  our  own  maple  sugar,  too,  I  have  frequently  eaten,  and  think 
its  flavour  peculiarly  agreeable. 

Mrs  B.  There  are  few  vegetables  which  do  not  contain  sugar(2),  but  it 
is  so  much  more  abundant  in  the  sugar  cane  (arundo  saccharifera)  than  in 
any  other  plant,  that,  excepting  under  particular  circumstances,  the  whole 
supply,  both  for  Europe  and  this  country,  is  obtained  from  it. 

Caroline.  I  have  read  the  description  of  the  mode  of  making  sugar  in 
the  West  Indies  and  in  Louisiana,  and  know  that  the  juice  of  the  cane  is 
pressed  out,  by  passing  it  between  large  iron  rollers;  after  which,  the  watery 
part  is  evaporated  by  boiling,  and  the  solid  part  collected  in  the  form  of 
brown,  or  moist  sugar(3). 

Mrs  B.  The  juice,  when  pressed  out  of  the  cane,  contains  a  portion  of 
vegetable  acid,  and  of  mucilaginous  matter,  which  requires  to  be  removed: 
this  is,  in  great  part,  effected,  during  the  boiling,  by  the  addition  of  lime- 
water,  the  lime  neutralizing  the  acid,  and  causing  much  of  the  foreign  matter 
to  rise  to  the  surface,  whence  it  is  taken  by  skimming.  The  juice,  when 
sufficiently  concentrated,  is  drawn  off  into  wooden  coolers,  in  which  the 
sugar  crystallizes.  It  is  then,  however,  of  a  very  dark  coloui*,  owing  to  the 


65.  What  is  coke,  and  for  what  purpose  is  it  used? 

1.  What  characterizes  the  vegetable  principles  constituting  the  third 
class? 

2.  Is  sugar  a  common  product  of  vegetables? 

3.  In  what  plant  is  it  most  abundant,  and  how  is  it  procured? 


ON  SUGAR,  HONEY,  GUM,  &c.  291 

presence  of  that  brown,  siropy  flufft,  molasses.  To  get  rid  of  this  it  is  put 
into  barrels,  the  bottoms  of  which  are  perforated  with  numerous  small 
holes,  through  which  the  molasses  gradually  drains  off.  The  common  brown 
sugar  is  thus  prepared  for  mai-ket(4). 

Emily.  But  a  considerable  portion  of  sugar  must  still  be  contained  in 
the  molasses,  as  its  taste  fully  indicates. 

Mrs  B.  Yes,  but  it  is  so  intimately  mixed  with  other  vegetable  matters, 
as  to  prevent  its  crystallization.  This  fluid,  however,  is  not  lost,  as  much 
of  it  is  used  with  articles  of  food,  and  large  quantities  are  employed  in  the 
distillation  of  rum(5). 

Loaf-sugar,  is  prepared  by  redissolving  the  brown  sugar,  and  refining 
it  in  such  a  way  as  to  remove  the  whole  of  the  molasses,  and  other  foreign 
matter:  it  is  then,  as  you  know,  a  solid  white  substance,  of  a  crystalline  tex- 
ture, and  of  a  pleasant,  simply  sweet  taste.  By  its  ultimate  analysis,  an 
atom  of  sugar  appears  to  consist  of  one  atom  of  carbon,  one  of  oxygen,  and 
one  of  hydrogen. 

Caroline.  And  in  what  way  is  it  converted  into  sugar-candy,  and  barley 
sugar,  which  seem  to  consist  principally  of  this  material? 

Mrs  B.  Sugar-candy  is  made  by  dissolving  sugar  in  water,  and  allowing 
the  water  to  evaporate  very  slowly;  the  sugar  is  then  deposited  in  large 
compact  crystals.  Barley  sugar  is  prepared  by  melting  sugar  over  the 
fire,  pouring  it  out  in  its  fused  state,  and  cutting  it  into  sticks.  It  is  usually 
flavoured  by  means  of  some  of  the  essential  oils(6). 

Honey,  which  the  industrious  bee  collects  from  various  flowers;  manna, 
which  is  a  concrete  juice  obtained  from  several  species  of  ash;  the  sugar  of 
grapes,  and  some  other  saccharine  materials,  although  they  contain  princi- 
ples very  analogous  to  sugar,  do  not  appear  to  derive  their  sweet  taste 
from  the  same  identical  ingredient.  The  sweet  matter  of  manna  has  been 
procured  in  a  separate  state,  and  has  received  the  name  of  mannite.  Most 
of  these  vegetable  juices,  as  they  ooze  or  are  expressed  from  the  plant,  con- 
tain considerable  portions  of  the  principle  called  gum,  or  mucilage(7}. 

Emily.  That  is  a  substance  with  which  we  are  well  acquainted,  particu- 
larly with  the  kind  called  gum  arabic.  Gum  is  also  very  common  on  the 
bark  of  the  plum  and  peach  tree. 

Mrs  B.  GUM,  which,  when  in  solution,  is  called  mucilage,  is  contained  in 
most  plants,  but  the  most  useful  is  that  which  is  obtained  from  a  species  of  the 
Acacia  tree  growing  in  Arabia,  whence  it  derives  its  name  of  gum  arabic.  It 
is  procured  in  such  quantities  as  to  be  exported  to  most  parts  of  the  world. 
It  contains  much  nutriment,  and  forms  a  considerable  part  of  the  food  of  the 
natives  of  those  countries  which  produce  it. 

Although  there  are  several  species  of  gum,  it  is  probable  that  they  all 
contain  the  same  principle,  and  that  they  derive  their  peculiar  properties  from 
the  different  vegetable  products  with  which  this  principle  is  combined  in  the 
respective  plants  by  which  it  is  furnished (8). 

Emily.  In  its  external  appearance,  gum  resembles  the  resins,  but  it 
differs  from  them  in  being  soluble  in  water,  whilst  they  are  insoluble. 

Mrs  B.  A  resin  will  be  precipitated  from  its  solution  in  alcohol,  if  water 
be  added  to  it,  and  a  solution  of  gum  in  water,  will,  in  like  manner,  be  de- 
composed by  the  addition  of  alcohol.  The  cause  of  the  precipitation  is  the 


4.  Relate  some  of  the  particulars  of  the  manufacture. 

5.  What  is  observed  respecting  the  sweet  taste  and  the  uses  of  molasses? 

6.  How  are  loaf-sugar,  sugar-candy,  and  barley-sugar  prepared? 

7.  What  is  observed  respecting  honey,  the  sugar  of  grapes,  and  manna? 

8.  Whence  is  gum  or  mucilage  obtained,  and  what  is  said  of  it? 


292  CONVERSATIONS  ON  CHEMISTRY. 

same  in  both  cases;  namely,  the  affinitjP  of  water  and  of  alcohol  for  each 
other  being  «uch  as  to  deprive  the  gum,  or  the  resin,  of  its  solvent. 

Caroline.  I  now  know  why  some  spirit  varnish  was  spoiled  by  my  pour- 
ing a  little  water  into  it.  The  resin  separated,  and  fell  to  the  bottom,  in 
consequence  of  the  water  depriving  it  of  the  alcohol  which  had  held  it  in 
solution(9). 

Mrs  B.  STARCH,  or  FECULA,  is  very  abundant  in  the  vegetable  kingdom. 
That  which  is  generally  used  is  obtained  from  wheat;  but  the  common,  and 
the  sweet  potato,  yield  it  in  large  quantities.  The  Indian  arrow  root  is 
only  a  very  pure  starch.  Tapioca  and  sago,  also,  are  chemically  the  same 
with  fecula,  but  somewhat  modified  and  altered  by  the  heat  employed  in  their 
preparation.  Starch  is  insoluble  in  cold  water,  although  hot  water  will 
dissolve  it  completely(lO). 

•Emily.  Starch,  as  we  buy  it,  appears  to  be  somewhat  crystalline  in  its 
form;  but  yet  its  texture  does  not  at  all  resemble  that  of  crystals. 

JVLrs  B.  This  appearance  is  a  consequence  of  its  contraction  in  the 
process  of  drying  in  the  manufactories.  You  have  often  in  dry  weather 
observed  hard,  clayey  paths  cracked  or  divided  in  a  similar  way (11). 

In  its  composition,  starch  is  very  nearly  allied  to  sugar,  and  may  be 
wholly  converted  into  saccharine  matter  by  boiling  it  in  water  containing  a 
small  portion  of  sulphuric  acid.  Frost  produces  a  similar  effect  upon  the 
fecula  contained  in  the  potato,  and  in  other  vegetables,  several  of  which,  you 
know,  acquire  a  peculiar  sweetness  by  being  frozen(12). 

When  seeds  begin  to  germinate,  their  starch  is  converted  into  sugar, 
which,  being  soluble^  becomes  the  food  of  the  embryo  plant.  In  the  process 
of  malting  barley,  the  grain  is  first  moistened,  and  allowed  to  sprout;  and 
then  heated  sufficiently  to  arrest  its  further  growth.  It  is  thus  rendered 
saccharine,  and  fitted  for  the  use  of  the  brewer  or  distiller(13). 

Caroline.  Although  starch  is  obtained  from  wheat,  the  difference  'be- 
tween it  and  flour  is  very  great.  I  think  that  starch  would  answer  but 
indifferently  in  the  hands  of  the  baker  or  of  the  cook,  for  making  loaves  or 
puddings. 

JMrs  B.  The  different  kinds  of  grain  contain  a  principle  called  GLTJTE^. 
This  principle  is  more  abundant  in  wheat  than  in  either  of  the  other  farina* 
ceous  plants.  The  soluble  materials,  and  the  fecula,  may  be  washed  out 
of  flour;  and  when  this  is  done,  the  gluten  will  be  obtained  in  a  separate 
state.  This  substance  is  very  tenacious  and  elastic,  of  a  gray  colour,  and 
fibrous  texture.  Like  animal  matter,  it  contains  nitrogen,  and  if  left  in 
a  moist  state  will  soon  putrefy.  The  tenacity  of  paste  made  from  wheat 
flour,  and  also  the  nutritious  quality  of  wheat  bread,  result  principally  from 
the  gluten  in  their  composition(l4).  Two  proximate  principles  have  been 
discovered  in  gluten,  one  of  which  has  been  named  ifliadm&,^{.he  other 
zymome. 

Caroline.  What  a  complex  affair  is  a  common  loaf  of  bread !  To  make 
it  we  have  to  take  the  fecula,  gluten  with  its  gliadine  and  zymome,  some 
water,  and  yeast,  a  portion  of  muriate  of  soda,  with  a  little  pearl  ash,  besides 
all  the  contaminations  of  all  these  ingredients;  we  mix  them  together,  and 
call  the  compound  simple  bread.  The  very  list  of  materials  would  supply 
a  column  for  a  dictionary (15). 


9.  By  what  properties  are  the  gums  and  resins  distinguished? 

10.  Whence  is  fecula  or  starch  obtained,  and  what  are  its  properties? 

'11.  What  causes  its  columnar,  or  crystal-like  appearance? 

12.  By  what  means  may  fecula  be  converted  into  sugar? 

13.  What  are  the  effects  of  germination,  and  what  is  malting? 

14.  Detail  the  properties  of  gluten,  and  the  mode  of  obtaining  it. 

15.  What  observation  is  made  respecting  the  composition  of  bread? 


ON  TANNIN,  LIGNIN,  AND  COLOURING  MATTER.     293 

J\frs  S.  We  shall  soon  dismiss  these  proximate  principles,  and  proceed 
to  the  spontaneous  decomposition  of  vegetables.  But,  before  doing  this, 
tannin,  lignin,  and  the  colouring  matters  of  plants,  will  claim  some  notice. 

TAHITI*  exists  in  large  quantities  in  all  astringent  plants,  and  may,  indeed, 
be  considered  as  their  astringent  principle.  It  is  sometimes  found  alone, 
but  is  more  frequently  accompanied  by  gallic  acid,  as  in  gall  nuts,  the 
bark  of  oak  and  other  trees,  in  the  unripe  persimmon,  and  in  tea. 
Like  gallic  acid,  it  precipitates  the  salts  of  iron  of  a  black  colour;  and  com- 
bined with  the  gallate  of  iron  forms  the  basis  of  writing  ink,  and  of  the 
usual  black  dyes.  Its  most  important  use,  however,  is  in  the  process  of 
tanning,  or  the  conversion  of  the  skins  of  animals  into  leather;  a  circum- 
stance which  I  shall  particularly  explain  when  we  treat  of  animal  chem- 
istry(16). 

Mr  Hatchett,  a  chemist  of  much  celebrity,  obtained  a  substance  bearing 
a  strong  resemblance  to  tannin,  by  digesting  charcoal  and  nitric  acid  to- 
gether. Their  product  has  been  named  artificial  tannin. 

Emily.    And  has  not  this  discovery  been  of  great  use  to  the  manufacturers  ? 

J\frs  JR.  Nature  furnishes  tannin  in  so  many  of  her  productions,  and  at 
so  little  cost,  that  were  the  artificial  exactly  like  the  natural  tannin,  still  its 
price  would  be  too  great  to  make  the  discovery  useful  in  an  economical  point 
of  view;  although,  as  a  scientific  fact,  it  may  be  of  real  importance(17). 

LiGNix,  or  the  WOODY  FIBRE,  constitutes  the  great  body  of  a  plant,  giving 
to  it  its  solidity  and  support,  as  the  animal  frame  is  sustained  by  the  bones. 

Emily.     It  must  be  from  the  Ugnin,  then,  that  common  charcoal  is  formed. 

Jlfrs  JB.  The  -woody  fibre,  as  a  proximate  principle,  consists  not  only  of 
carbon,  but  of  the  ordinary  constituents  of  vegetable  matter.  To  obtain  lig- 
nin  in  a  separate  state,  wood,  in  form  of  shavings  or  of  saw  dust,  is  alter- 
nately digested  in  water,  in  alcohol,  and  in  dilute  muriatic  acid:  all  the 
soluble  parts  will  be  thus  removed,  and  the  lignin  alone  remain.  It  has 
neither  taste  nor  smell,  and  undergoes  no  change  by  keeping.  Dry  wood  is 
said  to  contain  about  ninety-six  per  cent  of  lignin(18). 

By  digesting  lignin  for  some  time  with  sulphuric  acid,  it  is  changed  into 
a  substance  resembling  gum,  and  this  by  boiling,  may,  like  fecula,  be  con- 
verted into  sugar. 

Caroline.  One  of  the  last  articles  which  I  should  have  thought  of  trans- 
forming into  sugar,  would  have  been  saw  dust.  The  similarity  which 
exists  between  the  different  vegetable  compounds,  might,  however,  when 
duly  weighed,  induce  us  to  suspect  that  agents  which  have  the  power  to 
change  the  proportions,  or  alter  the  arrangement  of  the  atoms  of  their  ele- 
ments, might  sometimes  convert  one  of  these  vegetable  principles  into 
another(19). 

Mrs  B.  The  COLOURING  MATTER  found  in  plants  has  sometimes  been 
classed  as  a  distinct  principle;  but  colouring  materials  differ  so  much  from 
each  other  in  their  solubility,  and  in  their  other  properties,  as  to  render 
the  propriety  of  such  a  classification  very  doubtful.  The  colouring  matter 
is  always  attached  to  some  one  or  more  of  the  proximate  principles,  such  as 
the  mucilaginous,  farinaceous,  and  resinous.  These,  if  there  is  a  separate 
colouring  principle,  so  far  modify  its  properties  as  to  render  it  necessary 
to  treat  it  by  very  different  processes,  when  it  is  applied  in  the  arts  of  paint- 
ing or  dyeing(20). 


16.  What  are  the  sources,  properties,  and  uses  of  tannin? 

17.  What  is  said  respecting  the  discovery  of  artificial  tannin? 

18.  What  is  Ugnin,  and  how  is  it  obtained  in  a  separate  state? 

19.  What  is  said  on  the  conversion  of  lignin  into  sugar? 

20.  What  observations  are  made  on  the  colouring  principle3 

Z  2 


294  CONVERSATIONS  ON  CHEMISTRY. 

Emily.  The  LAKES,  I  believe,  are  all  of  them  vegetable  colours,  and 
most  of  them,  I  know,  are  fugitive  when  used  in  painting. 

Mrs  B.  The  lakes  consist  of  vegetable  colouring  matter,  combined 
with  alumine,  or  witli  some  other  metallic  oxide,  to  which  they  have  an 
affinity,  and  with  which  they  form  insoluble  compounds(21).  Some  of 
the  vegetable  colours  that  are  used  in  dyeing  will  at  once  attach  themselves 
to  the  fibres  of  the  material  to  be  dyed,  and  such  are  called  substantive 
colours;  but  many  of  them  will  impart  a  mere  stain,  which  is  readily 
washed  out,  and  these  are  denominated  adjective  colours.  To  cause  the  lat- 
ter to  attach  themselves  permanently,  the  cloth  to  be  dyed  is  first  dipped 
into  a  solution  of  some  substance  which  has  an  affinity  to  its  fibres,  and 
also  to  the  colouring  matter  which  is  to  be  employed.  When  this  has 
been  effected,  the  cloth  may  take  a  permanent  dye  in  a  liquid  that 
would  otherwise  scarcely  have  discoloured  it(22). 

Caroline.  Dyeing,  then,  must  be  a  chemical  art,  as  it  does  not,  like 
painting,  consist  in  merely  covering  a  substance,  mechanically,  with  colour- 
ing matter. 

Mrs  B.  Undoubtedly.  The  condition  required  to  form  a  good  dye,  is 
that  the  colouring  matter  should  be  precipitated,  or  fixed,  on  the  substance 
to  be  dyed,  and  should  form  a  compound  not  soluble  in  the  liquids,  or  re- 
movable by  the  other  agents  to  which  it  will  probably  be  exposed.  Thus, 
for  instance,  printed  or  dyed  linens  or  cottons  must  be  able  to  resist  the  ac- 
tion of  soap  and  water,  to  which  they  must  necessarily  be  subjected  in  wash- 
ing; and  woollens  and  silks  should  withstand  the  action  of  grease  and  acids, 
to  which  they  may  be  accidentally  exposed(23). 

Caroline.  Then  if  linen  and  cotton  have  not  a  sufficient  affinity  for  the 
colouring  matter,  the  combination  is  effected  by  the  intervention  of  a  third 
substance? 

Mrs  B.  Yes;  and  this  third  substance  is  called  a  mordant,  or  basis.  Many 
articles  to  be  dyed  are*dipped  into  a  solution  of  alum,  the  alumine  of  which 
has  an  affinity  for  the  substance  of  the  cloth,  and  attaches  itself  firmly  to  it. 
When  dipped  into  the  dyeing  liquid,  the  affinity  of  the  alumine  for  colouring 
mattei  :s  then  brought  into  operation,  and  the  colour  permanently  precipi- 
tated *lpon  the  cloth.  The  alumine  is,  in  this  case,  the  mordant,  or 
basis(24). 

Emily.  This  is  an  exemplification  of  the  fact  that  two  substances  which 
have  no  apparent  affinity  for  each  other,  may  be  made  to  combine  by  the 
intervention  of  a  third;  just  as  oil  and  water,  which  will  not  unite  when 
alone,  combine  and  form  soap  if  an  alkali  is  added  to  them(25). 

Mrs  B.  The  preceding  examples  of  the  compounds  secreted  by  the 
organs  of  plants,  will  suffice  to  give  you  a  clear  idea  of  their  general  pro- 
perties; and  we  will  now  proceed  to  investigate  some  of  the  effects  produced 
by  the  SPONTANEOUS  CHANGES  OF  VEGETABLE  MATTER.  You  are  already 
aware  that  the  simples  and  compounds  contained  in  vegetable  substances, 
enter  into  new  forms  of  existence,  when  they  are  no  longer  controlled  by  the 
living  principle.  The  examination  of  these  changes  will  present  a  wide  field 
for  investigation,  of  which  we  shall  be  able  to  explore  only  a  small  part. 

Caroline.  The  term  fermentation,  I  know,  is  applied  to  such  changes; 
but  it  appears  to  me  that  it  is  rather  indefinite,  as  the  effects  which  it  pro- 
duces are  so  various.  •  Thus  manure,  bread,  beer,  vinegar,  and  many  other 
articles,  are  said  to  ferment  when  they  are  undergoing  certain  changes;  but 

21.  How  are  the  vegetable  colours  called  lakes  obtained? 

22.  What  are  adjective  and  what  substantive  colours,  as  used  in  dyeing? 

23.  What  is  required  in  dyeing,  and  why  is  it  a  chemical  art? 

24.  What  is  a  mordant  or  basis,  and  what  does  it  effect? 

25.  What  law  of  chemical  affinity  does  it  serve  to  exemplify  ? 


ON  THE  SACCHARINE  AND  VINOUS  FERMENTATIONS.    295 

some  of  them  spoil  by  fermentation,  Avhilst  others  acquire  properties  which 
are  highly  valued  by  us(26). 

Mrs  B.  In  many  cases  of  fermentation,  there  is  a  visible  intestine  mo- 
tion in  the  materials  undergoing  the  process:  this  motion  is  occasioned  by 
the  extrication  of  gaseous  matter.  Sometimes,  however,  there  is  no  gaseous 
matter  evolved,  or  if  there  is,  the  change  takes  place  so  slowly  that  it  is  im- 
perceptible. As  the  vegetable  principles  vary  so  much  in  their  natures, 
their  operation  upon  each  other,  or  that  of  other  agents  upon  them,  must  ne- 
cessarily be  different;  and  this  has  given  rise  to  the  division  of  the  fermenta- 
tive process  into  four  kinds,  namely,  the  saccharine,  the  vinous,  the  acetous, 
and  the  putrefactive  fermentation(27). 

Emily.  These  terms  are  very  expressive,  as  they  evidently  point  to  the 
production  of  sugar,  of  wines  and  acids,  and  of  the  final  change  to  which  all 
vegetable  and  animal  materials  appear  to  be  liable. 

Mrs  B.  The  SACCHARINE  FERMENTATION  appears  principally  to  take 
place  infecula,  or  starch.  The  circumstances  under  which  it  occurs  have 
been  so  recently  noticed,  that  I  need  not  repeat  them(28).  I  shall  there- 
fore pass  at  once  to  the  second  kind,  which  is  the  VINOUS  FERMENTATION. 
Although  this  name  is  derived  from  the  fermentation  which  gives  rise  to  the 
production  of  wine,  it  is  the  same  process  which  takes  place  in  cider,  beer, 
and  other  liquids  when  they  acquire  an  intoxicating  property  by  being 
allowed  to  ferment,  and  they  are  all  included  under  the  general  name  of 
vinous  liquors(29). 

Caroline.  1  have  often  thought  it  a  curious  circumstance  that  we  may 
drink  a  large  quantity  of  sweet  cider,  without  any  danger  of  being  made  giddy 
by  it;  whilst  a  tumbler  of  fermented  eider  might  prove  a  little  too  much 
for  our  gravity. 

Mrs  B.  It  is  absolutely  necessary  to  the  production  of  the  vinous  fer- 
mentation that  saccharine  matter  should  be  present  in  the  liquid  which  is  to 
undergo  that  process.  The  juices  of  fruits  usually  contain  all  the  sugar 
that  is  necessary;  and  in  beer  and  ale  it  is  supplied  by  the  malting  of  the 
grain,  which  has  converted  its  starch  into  sugar.'  When  a  fluid  containing 
the  necessary  ingredients  is  exposed  to  a  temperature  of  from  sixty  to  sev- 
enty degrees  of  heat,  the  operation  soon  commences.  Bubbles  of  gas  escape 
from  it,  and  presently  the  whole  volume  of  the  liquid  is  in  brisk  motion;  its 
appearance  is  turbid,  its  surface  covered  with  froth,  and  its  temperature 
•will  be  found  to  have  risen  severaldegrees  above  that  of  the  surrounding 
air.  After  the  lapse  of  a  few  days,  the  gas  ceases  to  escape,  the  temperature 
falls,  the  impurities  subside,  and  the  liquor  becomes  clear  and  transparent. 
The  process  is  then  considered  as  completed,  and  the  properties  of  the  1L» 
quid  are  completely  altered(SO). 

Emily.  And  what  are  the  precise  changes  which  occur  during  this  fer- 
mentation? 

Mrs  B.  A  large  part  of  the  sugar  has  disappeared,  and,  in  its  stead,  al» 
cohol  has  been  formed,  which  being  mixed  in  the  fluid  communicates  to  it 
its  stimulating  and  intoxicating  properties(Sl). 

Caroline.  And  is  sugar  all  that  is  necessary  to  this  fermentation?  If  so, 
sugar  and  water  may  be  converted  into  spirit. 

Mrs  B.  Although  it  is  the  sugar  only  that  is  decomposed,  something  else 
is  necessary  to  cause  the  fermentation  to  begin.  The  mucilage,  and  other 


26.  What  remarks  are  made  on  the  use  of  the  term  fermentation? 

27.  What  takes  place  in  fermentation,  and  what  kinds  are  named? 

28.  In  what  principle  does  the  saccharine  fermentation  occur? 

29.  What  is  said  of  the  vinous  fermentation  and  vinous  liquors? 

30.  What  are  the  circumstances  attendant  on  the  vinous  fermentation? 

31.  What  are  the  precise  changes  effected  by  it? 


296  CONVERSATIONS  ON  CHEMISTRY. 

'*      •'*! 
principles  existing  in  the  juices  of  fruits,  suffice  for  this  purpose;  hut  if  sugar 

alone  be  contained  in  the  water,  it  is  necessary  to  add  some  yeast,  -which  is 
itself  a  peculiar  product  of  fermentation,  and  is  specially  adapted  to  pro- 
mote it.  By  this  addition,  sugar  and  water  may  be  actually  converted  into 
spirit  and  water  (52). 

Caroline.  1  have  often  heard  of  the  distillation  of  spirits  from  potatoes, 
and  from  other  roots,  as  well  as  from  grain,  and  the  juices  of  fruits:  in  this 
case  it  would  seem  that  spirit  may  be  formed  without  the  presence  of  sugar. 

Mrs  B.  But  all  these  substances  contain  a  considerable  quantity  of 
starch,  which  first  undergoes  the  saccharine  fermentation,  and  thus  furnishes 
the  sugar  necessary  to  the  vinous(33). 

The  manner  in  which  the  ardent  spirit,  or  alcohol,  is  separated  from  the 
fermented  liquor,  I  described  to  you  in  one  of  our  early  conversations, 
(p.  62),  and  showed  you  an  alembic,  or  still.  I  need  not,  I  am  sure,  repeat 
•what  I  then  said(34). 

Emily.  You  have  not  informed  us,  Mrs  B.,  in  what  the  decomposition  of 
the  sugar  consists,  or  what  is  the  kind  of  gas  disengaged  in  this  fermenta- 
tion. I  know  enough,  however,  about  breweries  and  distilleries  to  be  at  no 
loss  on  the  latter  point;  besides  which,  I  now  recollect  that  you  told  us, 
some  time  since,  that  the  gas  in  question  was  carbonic  acid. 

Mrs  B.  An  atom  of  alcohol  consists  of  one  atom  of  oxygen,  united  to 
two  of  carbon  and  three  of  hydrogen.  When  by  fermentation  a  portion  of 
the  sugar  is  converted  into  carbonic  acid,  the  remaining  ingredients  are  in 
the  precise  proportions  for  forming  alcohol,  which  is,  consequently,  the  re- 
sult of  this  decomposition(35). 

Caroline.  Pray  what  is  meant  by  proof  spirit?  I  know  that  it  relates  to 
its  strength,  but  do  not  fully  understand  the  meaning  of  the  term. 

Mrs  B.  When  a  vinous  liquid  has  been  so  far  rectified  by  distillation  as 
to  contain  about  equal  parts  of  alcohol  and  water,  it  is  then  called  proof 
spirit.  When  of  greater  strength,  it  is  named  second,  third,  or  fourth  proof, 
according  to  its  state  of  concentration;  and  when  as  much  as  possible  of  the 
water  has  been  separated  from  it,  it  is  then  spirits  of  -wine,  or  rather  alco* 


Jllcohol,  you  know,  is  extremely  inflammable.  When  burnt,  it  is,  from 
the  nature  of  its  constituents,  wholly  converted  into  water  and  carbonic  acid, 
and  it  is  a  fact  which  a  person  ignorant  of  chemistry  would  scarcely  credit,  that 
either  of  the  products  of  its  combustion  will  considerably  outweigh  the  al- 
cohol which  has  been  burnt. 

Emily.  Because  both  its  carbon  and  its  hydrogen  obtain  oxygen  from, 
the  atmosphere,  with  which  they  combine,  and  thus  acquire  the  additional 
weight(37). 

Mrs  B.  Although  ETHER  is  not  produced  by  the  spontaneous  decomposi- 
tion of  vegetable  matter,  but  is  artificially  obtained  by  the  decomposition  of 
alcohol,  I  shall  now  give  you  some  account  of  its  formation.  The  experi- 
ments which  we  have  performed  with  it  have  rendered  you  familiar  with  its 
volatility,  and  also  with  the  facility  with  which  it  takes  fire  and  burns. 
There  are  several  species  of  ether,  produced  by  the  action  of  different  acids 
upon  alcohol:  the  most  common,  however,  is  sulphuric  ether,  and  to  this 
we  shall  confine  our  remarks(38).  Do  you  recollect  how  we  obtained  the 
defiant  or  heavy  carburetted  hydrogen  gas  ? 

.  _  . 
•  -  • 

32.  What  is  necessary  to  the  commencement  of  this  fermentation? 

33.  What  is  observed  on  distilling  spirits  from  potatoes,  &c.  ? 

34.  Explain  the  nature  of  distillation,  as  described  at  page  62. 

35.  What  are  the  atomic  changes  when  alcohol  is  produced? 

36.  What  is  meant  by  proof  spirits  and  by  alcohol? 

37.  What  is  observed  respecting  the  combustion  of  alcohol? 

38.  How  are  the  different  kinds  of  ether  produced  from  alcohoP 


ON  THE  ACETOUS  FERMENTATION.  297 

Caroline.  Oh  yes.  The  experiment  was  too  striking  to  he  so  soon  for- 
gotten. To  procure  the  gas  you  decomposed  alcohol  by  the  agency  of  sul- 
phuric acid. 

Mrs  JB.  And  by  a  similar  process  ether  is  obtained,  only  the  decompo- 
sition is  not  carried  so  far  in  the  latter  case  as  in  the  former.  Whilst  an 
atom  of  alcohol  consists  of  one  atom  of  oxygen,  two  of  carbon,  and  three  of 
hydrogen,  ether  is  composed  of  one  atom  of  oxygen,  four  of  carbon,  and  five 
of  hydrogen.  It  differs  from  alcohol  therefore  in  containing  a  less  quantity 
both  of  oxygen  and  hydrogen  in  proportion  to  the  carbon.  To  convert 
alcohol  into  ether,  it  is  boiled  in  a  retort  with  sulphuric  acid;  the  affinity  of 
this  fluid  for  water  enables  it  to  abstract  one  half  of  that  which  enters  into 
the  composition  of  the  alcohol,  when  the  regaining  atoms  are  in  such  proper- 
tions  as  by  their  combination  to  form  ether(39). 

I  will  now  exhibit  to  you  a  very  curious  in- 
stance  of  the  combustion  of  the  vapour  of  alcohol 
or  ether. 

Emily.  The  little  lamp  which  you  have  placed 
upon  the  table  has  its  wick  surrounded  by  a  coil 
of  wire,  which  appears  like  silver. 

Mrs  J3.  The  wire  is  platinum,  and  the  lamp 
is  called  the  aphlogistic  or  Jlameless  lamp.  It 
depends  for  its  operation  upon  an  interesting  fact 
discovered  by  Sir  Humphry  Davy,  that  if  a  coil 
of  platina  wire  is  heated,  and  then  held  near  the 
surface  of  ether  or  of  alcohol,  in  a  glass,  it  will  be- 
come of  a  glowing  red  heat,  and  will  continue  so 
until  the  whole  of  the  ether  or  the  alcohol  has  eva- 
porated. I  have  some  ether  in  this  lamp;  I  will 
light  the  wick,  and  then  blow  it  out,  and  you  will 
perceive  the  effect  produced  upon  the  platina  wire. 

Caroline.  It  is  extremely  curious;  the  wire  does  indeed  continue  red 
hot,  and  that  without  any  apparent  cause,  as  there  is  no  flame. 

Mrs  JB.  The  vapour  of  the  ether  burns  as  it  escapes,  but  not  with  sufficient 
heat  to  cause  it  to  inflame,  although  with  enough  to  keep  the  wire  red  hot, 
•which  in  its  turn  continues  this  flameless  combustion  of  the  ether(40). 

We  will  now  converse  awhile  about  the  formation  of  acetic  acid,  the 
principle  which  communicates  a  sour  taste  to  vinegar. 

Emily.  We  very  well  know  the  effect  of  this  fermentation  upon  our 
beer  and  cider,  although  we  have  much  to  learn  respecting  its  chemical  na- 
ture. It  seems  however  that  this  fermentation  succeeds  to  the  vinous. 

Mrs  JB.  The  ACETOUS  FERMENTATION  does,  as  you  observe,  succeed  to 
the  vinous;  and  in  some  instances  so  quickly  that  it  is  difficult  to  complete 
the  one  before  the  commencement  of  the  other.  The  acetous  fermenta- 
tion consists  in  the  decomposition  of  the  alcohol  formed  in  the  vinous,  and 
its  conversion  into  acetic  acid(kl). 

Caroline.  But  alcohol  contains  so  little  oxygen,  that  it  is  difficult  to  con- 
ceive how  it  can  become  an  acid,  unless  it  should  be  one  of  the  hydraeids. 

Mrs  B.  The  acetous  fermentation  requires  the  exposure  of  the  liquid 
to  the  action  of  the  atmosphere,  from  which  it  absorbs  a  large  portion  of 
oxygen.  The  appearances  which  accompany  this  fermentation  are  in  seve- 
ral respects  similar  to  those  which  accrue  in  the  vinous,  and  it  is  effected 
at  the  same  degree  of  temperature.  Although  the  internal  motion  is  less 
violent,  it  still  exists,  and  is  accompanied  by  an  escape  of  carbonic  acid;  the 


39.  Give  the  process  for  the  formation  of  sulphuric  ether. 

40.  Describe  the  structure  and  operation  of  the  aphlogistic  lamp. 

41.  What  fermentation  follows  the  vinous,  and  what  does  it  produce? 


298  CONVERSATIONS  ON  CHEMISTRY. 


temperature  of  the  liquor  rises,  and  it  becomes  at  first  turbid,  and  afterwards 
clear.  When  the  process  is  completed  not  an  atom  of  alcohol  remains,  the 
whole  being  converted  into  acetic  acid(42). 

Emily.  Pray  what  is  the  precise  difference  between  vinegar  and  acetic 
acid? 

Mrs  B.  Vinegar  is  sometimes  made  from  wine,  sometimes  from  cider, 
beer,  infusions  of  sugar  or  molasses  in  water,  or  other  similar  mixtures,  to 
Xvhich  yeast  or  some  other  ferment  is  added.  When  the  acid  is  formed,  it 
is  necessarily  mixed  with  whatever  vegetable  matter  the  liquid  contained, 
and  receives  different  flavours  according  to  the^lifference  in  these  materials: 
this  mixture  constitutes  vinegar.  Its  sour  taste,  however,  is  derived  ex- 
clusively from  acetic  acid,  which  we  can  obtain  in  a  separate  state.  Its 
taste  is  then  simply,  but  intensely,  acid(43). 

A  very  fine  vinegar  is  now  prepared  from  what  has  been  called  the  pyro- 
Ugneous  acid.  When  wood  is  converted  into  charcoal  in  close  vessels,  for 
the  purpose  of  manufacturing  gunpowder,  if  the  vapour  that  escapes  from  it  is 
condensed,  it  forms  an  extremely  acid  liquor,  which  has  received  the  name 
of  pyroligneous  acid:  the  fluid  thus  procured  contains  tar,  and  several  other 
impurities.  The  acid  when  separated  from  these  impurities  is  found  to  be 
the  acetic.  The  process  of  preparing  it  has  been  brought  to  great  perfection, 
and  a  very  fine  vinegar  is  now  obtained  from  it(44). 

Caroline.  There  is  one  common  fermentation  which  scarcely  appears  to 
belong  to  either  of  those  which  you  have  mentioned,  and  it  certainly  does 
not  appertain  to  the  putrefactive:  I  mean  the  fermentation  of  bread. 

Mrs  B.  Tliis  at  one  time  was  called  the  pannary  fermentation,  and 
was  believed  to  be  peculiar  in  its  character.  The  prevalent  opinion  now 
is  that  it  is  identical  with  the  vinous.  The  yeast  acting  upon  the  fecula, 
produces  the  saccharine  and  vinous  fermentations;  carbonic  acid  is  disen- 
gaged, which,  being  entangled  by  the  dough,  causes  it  to  rise,  as  it  is  called, 
by  filling  it  with  numerous  air  bubbles,  which  give  to  it  its  spongy  texture, 
or  lightness.  In  proof  of  the  truth  of  this  theory,  alcohol  has  actually 
been  detected  in  dough(45). 

Caroline.  I  believe  that  the  putrefactive  fermentation  completes  your 
list  of  these  processes,  and  that  it  is  the  termination  of  the  vegetable  exist- 
ence, completely  undoing  the  work  which  organization  had  effected. 

Mrs  B.  The  PUTREFACTIVE  FERMENTATION,  although  more  strongly 
marked,  and  more  rapid,  in  animal  than  in  vegetable  substances,  does  evi- 
dently take  place  in  the  latter.  Moisture,  a  sufficient  degree  of  heat,  and 
access  of  air,  are  necessary  to  this  process.  The  principal  solid  product  is 
vegetable  mould,  which  consists  of  carbon,  combined  with  some  oxygen  and 
hydrogen;  water,  a  little  acetic  acid,  and  probably  some  oily  matter  con- 
stitute the  fluids;  and  carbonic  acid  and  light  carburetted  hydrogen,  the  gases. 
But  from  those  plants  which  contain  nitrogen,  sulphur,  or  phosphorus,  pro- 
ceed ammonia,  and  portions  of  some  other  compound  gases,  resembling  those 
which  were  noticed  at  an  early  part  of  our  last  conversation,  as  resulting 
from  the  decay  of  animal  matter(46). 

Emily.,  We  have  traced  these  substances  to  their  state  of  final  disorgan- 
ization, and  it  would  be  delightful  now  to  follow  them  to  their  resuscitation 
in  new  forms,  giving  organization,  life,  and  beauty  to  other  vegetable  be- 
ings, of  which  they  are  prepared  to  become  the  nutriment 

Mrs  B.     This  would  certainly  be  a  most  worthy  object  of  inquiry;  but 


42.  Relate  the  circumstances  attendant  on  this  fermentation. 

43.  In  what  consists  the  difference  between  vinegar  and  acetic  add? 

44.  How  is  pyroligneous  acid  procured,  and  what  is  its  nature? 

45.  What  is  observed  respecting  the  fermentation  of  dough? 

46.  What  are  the  general  products  of  the  putrefactive  fermentation? 

*"i 

-  -« 

. 

•-'"".          .3 


ON  ANIMAL  CHEMISTRY.  299 

t  belongs  to  the  department  of  vegetable  physiology,  rather  than  to  that 
>f  chemistry.  This  subject  has  been  so  ably  and  agreeably  treated  by 
WErs  Marcet  in  her  "Conversations  on  Vegetable  Physiology,"  that  I  can 
>romise  you  equal  pleasure  and  advantage  from  a  careful  perusal  and  study 
of  that  work. 


CONVERSATION  XXX. 

ON  ANIMAL  CHEMISTRY. 

The  Constituent  Principles  of  Jlnimal  Matter  found  in  Vegetables. 
Their  Proximate  Principles  more  Complex.  Fibrin.  Albumen.  Fining 
of  Wine,  Coffee,  &c.  Gelatin,  Glue,  and  IcthyoColla.  Osmazome.  Pro- 
cess of  Tanning.  Acids  existing  in  the  Jlnimal  System.  Jlnimal  Oils 
and  Fats.  Stearine  and  Elaine.  Margaric  and  Oleic  Jlcids.  Glycerine. 
Jldipocere.  Formation  of  Oils  from  their  Constituents.  Milk,  Cream, 
Casseous  Matter  or  Curd,  Whey,  and  Rennet. 

Mrs  B.  We  have  now,  young  ladies,  arrived  at  the  last  division  of  our 
subject,  ANIMAL  CHEMISTRT.  In  this  department  are  comprehended  the 
most  complex  and  wonderful  of  all  the  Creator's  works.  The  proximate 
principles  found  in  the  beings  which  form  this  kingdom,  although  less  nu- 
merous than  those  of  vegetables,  are  still  more  dependent  upon  the  control 
of  that  mysterious  principle,  life;  as  the  large  quantity  of  nitrogen  which 
most  of  them  contain,  gives  them  a  constant  tendency  to  undergo  the  putre- 
factive fermentation,  in  which  those  extremely  offensive  gases  are  disen- 
gaged which  distinguish  the  rapid  decay  of  animal  matter(l). 

Emily.  As  all  animals  ultimately  derive  their'nourishment  from  vege- 
tables, it  seems  strange  that  they  should  be  more  complex  in  their  compo- 
sition than  the  substances  upon  which  they  depend  for  sustenance. 

Mrs  B.  All  the  constituent  materials  of  the  animal  economy  have  ac* 
tually  been  discovered  in  certain  vegetables.  Nitrogen  exists  in  wheat,  and 
in  many  other  plants.  But  animals  are  surrounded  by  an  atmosphere  in 
•which  this  principle  abounds,  and  from  which  they  might  obtain  it  were  it 
entirely  absent  from  their  food(2).  Besides  the  oxygen,  hydrogen,  carbon^ 
and  nitrogen  which  animal  substances  contain,  sulphur,  phosphorus,  iron, 
lime,  and  other  earthy  as  well  as  saline  ingredients  are  found  in  them,  in 
notable,  and  sometimes  in  very  considerable  quantities.  Each  of  them  also 
has  been  discovered  in  certain  plants.  It  is  in  the  proportionate  quantities, 
and  the  mode  of  combination,  therefore,  that  the  difference  between  animal 
and  vegetable  products  principally  consists(S). 

Caroline.  I  am  glad  that  the  proximate  principles  of  animal  matter, 
although  more  complex,  are  not  equally  numerous  with  those  of  vegetables, 
as  we  may  the  more  readily  become  acquainted  with  them. 

Mrs  B.  The  first  of  the  animal  products  which  I  shall  describe  is 
FIBHIX.  This  constitutes  the  principal  part  of  the  flesh,  or  muscles,  and  is 
contained  also  in  large  quantities  in  the  blood.  Fibrin  may  be  obtained  by 
digesting  lean  meat  in  successive  portions  of  water  until  all  the  colouring 


1.  In  what  do  the  animal  principles  differ  from  those  of  vegetables? 

2.  What  are  the  sources  from  which  animals  may  derive  their  con 
stitueots? 

3.  What  further  is  remarked  respecting  these  combinations? 


, 
300  CONVERSATIONS  ON  CHEMISTRY. 

matter  is  discharged,  and  the  soluble  portion  dissolved(4).  It  then  appears 
as  a  white,  fibrous  substance,  which  is  insipid,  inodorous,  and  insoluble  in 
water  at  common  temperatures. 

Fibrin  when  moist  possesses  some  elasticity,  but  when  dried  it  becomes 
hard,  brittle,  and  semi-transparent.  If  allowed  to  remain  in  a  moist  stato 
it  soon  putrefies,  especially  in  warm  weather(5). 

Caroline.  As  fibrin  is  the  basis  of  the  muscles,  it  must  be  among  the 
most  abundant  of  the  animal  principles. 

JMrs  B.  It  is  so;  but  there  are  two  others,  albumen  and  gelatine,  which 
are  found  in  most  parts  of  the  system,  although  in  smaller  quantities  than 
fibrin. 

ALBUMEN  may  be  seen,  in  a  form  almost  pure,  in  the  white  of  an  egg. 
The  serum,  or  white  part,  of  the  blood  also  contains  a  large  portion  of  it, 
and  the  same  may  be  said  of  the  fluid  which  serves  to  lubricate  the  joints. 
In  these  instances  it  exists  in  the  fluid  state;  but  it  also  forms  a  part  of 
many  of  the  solids,  such  as  the  skin,  and  the  membranous  coating  of  the  va- 
rious  vessels.  Its  most  distinguishing  property  is  its  coagulating  when 
heated;  and  a  similar  change  is  produced  in  it  by  the  action  of  acids,  of 
alcohol,  and  of  some  other  agents(6). 

Emily.  This  coagulation  by  heat  is  familiar  to  us  in  the  white  of  the 
egg,  which,  unlike  most  other  substances,  becomes  harder  by  boiling. 

•Mrs  B.  Albumen,  when  pure,  coagulates  at  a  temperature  of  one  hun* 
dred  and  sixty  degrees,  and  when  diluted  with  water  it  undergoes  the  same 
change  at  the  boiling  point.  Even  when  mixed  with  one  thousand  times  its 
weight  of  water,  the  temperature  of  two  hundred  and  twelve  degrees  will 
render  the  water  milky  and  opake(7). 

Emily.  I  suppose,  then,  it  must  be  this  property  of  coagulating  which,  in 
some  way,  causes  the  white  of  the  egg  to  clear  coffee  and  other  liquids. 

•Mrs  B.  It  is.  When  the  white  of  an  egg  is  mixed  with  coffee,  it  coagni 
lates  by  boiling;  this  renders  it  insoluble,  in  consequence  of  which  it  falls 
to  the  bottom,  entangling  and  carrying  down  with  it,  those  minute  particles 
which  would  otherwise  render  the  liquid  turbid.  Albumen  is  mixed  with 
wine  for  a  similar  purpose.  The  acid  and  the  alcohol  contained  in  the 
wine,  conspire  in  producing  the  same  kind  of  coagulation,  and  in  this  way 
the  wine  is  fined  or  rendered  clear(8). 

Caroline.  I  have  often  observed  the  peculiar  effect  produced  upon  a 
silver  spoon,  when  left  standing  in  a  boiled  egg;  it  becomes  not  onlf  tar- 
nished, but  sometimes  almost  black.  In  what  way  can  albumen  produce 
such  an  effect? 

Jlfrs  B.  Albumen,  as  found  in  the  white  of  the  egg,  contains  a  small 
portion  of  sulphur,  which,  when  the  egg  is  boiled,  unites  to  hydrogens  and 
produces  sulphuretted  hydrogen  in  sufficient  quantity  to  produce  the  effect 
of  which  you  speak.  Silver  and  some  other  metals  are  attacked  and  black- 
ened by  this  gas(9). 

The  third  of  these  most  prevalent  animal  compounds,  is  GELATIXE,  or 
JELLY.  This  is  the  chief  ingredient  of  the  skin,  and  it  is  largely  contained 
also  in  the  cartilages,  tendons,  membranes,  and  bones.  From  these  sub- 
stances boiling  water  separates  and  dissolves  it.  The  solution,  thus  obtained, 
becomes  more  or  less  solid,  on  being  allowed  to  cool,  and  receives  the 


4.  What  is  fibrin,  and  how  may  it  be  separately  obtained? 

5.  JBy  what  properties  is  it  distinguished? 

6.  In  what  substances  is  albumen  found,  and  what  are  its  properties > 

7.  At  what  temperature  does  albumen  coagulate? 

8.  How  does  it  operate  in  clearing  coffee,  and  in  fining  wine? 

9.  From  what  cause  does  an  egg  blacken  a  silver  spoon? 


OX  GELATINE.  301 

names  of  glue,  size,  or  jelly ,  according  to  its  consistence,  and  the  purpose 
to  which  we  design  to  apply  it(10). 

Caroline.  But  surely  common  glue,  and  calves'  foot  jelly  are  not  ex- 
actly the  same  substance. 

Mrs  JB.  Their  property  of  forming  a  jelly  when  cold  depends  entirely 
upon  the  presence  of  the  same  principle,  gelatine.  Glue  is  made  by  boiling 
the  ears,  feet,  and  refuse  cuttings  of  the  skins  of  animals  in  water,  and  evapo- 
rating the  fluid  to  such  an  extent,  that,  on  cooling,  it  should  form  a  very  hard 
jelly.  This  is  afterwards  cut  into  slices,  and  dried  on  netting  stretched  upon 
frames.  The  only  difference  between  this  and  the  jelly  from  calves'  feet,  or 
from  isinglass,  is  the  freedom  of  the  latter  substances  from  the  impurities 
•which  accompany  the  former(ll). 

Emily.  I  have  understood  that  isinglass,  which  is  sometimes  called^sA 
glue,  is  furnished  by  some  species  of  sturgeon,  but  from  what  part  of  the 
fish  I  do  not  recollect. 

Mrs  JB.  Its  most  proper  name  i&ichthyocolla.  It  consists  of  the  membra- 
nous sounds  of  several  fishes  of  the  sturgeon  kind,  and  being  a  very  pure 
species  of  .gelatine,  it  is  frequently  employed  where  culinary  preparations 
of  jelly  are  required(12). 

The  horns  and  hoofs  of  all  animals  yield  a  considerable  quantity  of  ge- 
latine; the  earthy  matter  of  the  bones  is  completely  penetrated  by  it.  When 
such  substances  are  boiled  in  water,  especially  after  being  reduced  into  small 
fragments,  or  shavings,  the  gelatine  is  separated  from  them,  in  consequence 
of  its  great  solubility(lS). 

Caroline.  Does  not  the  nutritious  property  of  soup  depend  entirely 
upon  the  gelatine  which  it  contains?  Rich  soup,  I  have  observed,  always 
forms  a  jelly  when  it  is  cold. 

Mrs  B.  All  the  soluble  parts  of  the  flesh  and  bones,  used  in  the  mak- 
ing of  soup,  are  contained  in  it,  and  the  portion  of  gelatine  is  usually 
considerable;  but  pure  gelatine  is  without  taste  or  smell,  and  you  would 
not  speak  very  highly  of  soup  which  resembled  it  in  these  particulars.  The 
characteristic  taste  and  odour  of  soup  depend  upon  the  presence  of  a  pecu- 
liar principle  which  is  called  OSMAZOME.  This  is  a  soluble  substance  of  a 
yellowish  brown  colour,  and  which  has  no  tendency  to  solidify  when 
cold(!4). 

Emily.  We  must  not  forget  that  the  explanation  of  one  of  the  important- 
properties  of  tannin,  was  deferred  until  we  had  acquired  some  knowledge 
of  gelatine. 

Mrs  J3.  I  am  gratified  at  your  reminding  me  of  this  fact.  You  are 
aware  that  the  conversion  of  the  skins  of  animals  into  leather,  is  performed 
by  a  process  called  tanning.  In  this  process  a  chemical  union  is  formed 
between  the  tannin  which  is  contained  in  the  bark  of  certain  trees,  (particu- 
larly that  of  the  oaks),  and  the  gelatine  which  forms  the  principal  ingredient 
in  the  skins  of  animals(15). 

Emily.     Pray  how  is  this  operation  performed? 

Mrs  JB.  After  the  removal  of  the  hair,  the  skin  is  exposed  to  the  action 
of  a  solution  of  tannin,  derived  from  substances  containing  considerable  quan- 
tities of  this  principle,  and  which  are  disposed  to  yield  it  readily.  The  usual 
method  is  to  infuse  coarsely  powdered  oak  bark  in  water,  and  to  keep  the 


'  10.  In  what  parts  isgelatine  contained,  and  what  property  distinguishes  it? 

11.  From  what  is  common  glue  made,  and  how  is  it  manufactured? 

12.  What  is  icthyocoila,  and  from  what  animals  is  it  procured? 

13.  From  what  other  parts  of  animals  may  gelatine  be  obtained? 

14.  From  what  substance  are  the  odour  and  flavour  of  soup  derived? 

15.  In  what  does  the  process  called  tanning'  consist? 

2  A 


302  CONVERSATIONS   ON  CHEMISTRY. 

skin  immersed  in  this  infusion  for  a  certain  length  of  time(16).  Daring  the 
performance  of  this  process,  which  is  slow  and  gradual,  the  skin  is  found  to 
increase  in  weight,  to  acquire  considerable  tenacity,  and  to  become  nearly 
impermeable  to  water.  The  effect  may  he  much  accelerated  by  using  solu- 
tions strongly  saturated  with  the  tanning  principle,  (which  can  be  extracted 
from  hark),  instead  of  employing  the  bark  itself.  But  this  quick  mode  of 
preparation  does  not  appear  to  make  leather  equally  good  with  that  obtained 
more  slowly(17). 

Caroline.  Then  the  effect  of  tannin,  upon  the  skins  of  animals,  is  to 
render  their  gelatine  insoluble  in  water? 

Mrs  B.  Such  is  the  change  produced,  and  you  have  in  this  case  an  ex- 
ample of  the  combination  of  two  soluble  substances,  tannin  and  gelatine* 
uniting  together,  and  forming  an  insoluble  material,  leather(18). 

Caroline.  I  wish  the  chemist  had  found  some  other  name  for  tannin;  it 
so  closely  resembles  that  of  the  process  of  tanning,  that  I  have  always  to 
pause  in  order  to  ascertain -which  of  the  two  is  the  subject  of  remark,  the 
effect  produced,  or  one  of  the  agents  necessary  to  its  production. 

Emily.  If  leather  consists  of  tannin,  combined  with  glue,  might  it  not  be 
manufactured  by  mixing  these  two  materials  together? 

Mrs  B.  I  have  in  one  of  these  glasses  an  infusion  of  gall  nuts,  which 
consists  in  great  part  of  tannin,  and  in  the  other,  some  glue  diffused  in 
water;  I  will  pour  these  together,  that  you  may  observe  the  effect  pro- 
duced. 

Caroline.  What  a  copious  precipitation!  How  imeadily  you  have  convert- 
ed the  two  into  leather(19). 

Mrs  B.  Chemically  speaking  the  compound  is  leather;  but  then  it  is 
leather  divided  into  minute  particles.  Were  we  to  press  these  particles 
together,  we  might  form  them  into  a  sheet  like  paper;  but  even  then  it 
would  possess  little  tenacity,  as  it  would  not  have  the  fibrous  structure  of 
the  organized  skin,  which  is  necessary  to  give  to  leather  that  toughness  and 
strength  without  which  it  would  be  of  no  value(20). 

An  infusion  of  gall  nuts  is  so  delicate  a  test  for  gelatine,  as  to  precipitate 
it  although  the  gelatine  may  be  mixed  with  five  thousand  times  its  own 
weight  of  water(21).  We  must  now  dismiss  gelatine  and  examine  some 
other  of  the  animal  compounds. 

Emily.  We  frequently  hear  of  acidity  in  the  animal  system;  there  is, 
therefore,  I  suppose,  a  class  of  animal  acids.  All  the  simple  substances 
which  exist  in  vegetables,  are  found  in  animal  matter  also,  and  are  likely 
therefore  to  form  analogous  combinations. 

Mrs  B.  Portions  of  the  sulphuric,  phosphoric,  muriatic,  and  acetic 
acids,  are  found  in  the  animal  system;  hut  it  also  contains  others  which  be- 
long exclusively  to  it(22).  Like  the  general  animal  products,  however, 
the  animal  acids  are  fewer  in  number  than  those  found  in  vegetables;  nor 
are  they  of  equal  importance.  Acids  are  not  unfrequently  the  pro- 
dn'^ts  of  diseased  action,  or  of  the  decomposition  of  animal  substances:  they, 
however,  are  not  of  a  nature  to  require  our  attention(23).  The  most 
remarkable  of  the  acids  belonging  to  the  animal  kingdom,  are  those  which 


16.  What  is  the  method  usually  pursued  by  the  tanner? 

17.  What  changes  occur  in  the  skin,  and  is  the  operation  rapid? 

18.  What  is  exemplified  by  the  union  of  tannin  and  gelatine? 

19.  What  experiment  is  mentioned  of  mixing  two  infusions? 

20.  What  is  remarked  respecting  the  substance  produced? 

21.  What  is  mentioned  respecting  the  infusion  of  gall  nuts  as  a  test? 

22.  What  acids  are  found  existing  in  animals? 

23.  What  is  remarked  respecting  some  other  acids? 


ON  ANIMAL  OILS  AND  FATS.  303 

exist  in  the  animal  oils  and  fats,  or  which  are  formed  by  them  when  they 
are  converted  into  soap,  or  submitted  to  other  chemical  processes. 

Caroline.  Although  I  know  that  the  animal  oils  combine  with  alkalies, 
and  thus  exhibit  one  of  the  characteristic  properties  of  acids,  still  they  are 
among  the  last  of  the  animal  products  in  which  I  should  have  looked  for 
them(24). 

Mrs  B.  You  will  presently  find  that  the  combinations  to  which  you 
have  alluded  are  actually  those  of  acids  and  alkalies,  and  that  soap,  there- 
fore, strictly  speaking,  may  be  placed  among  the  salts. 

The  ANIMAL  OILS  and  FATS  do  not  contain  nitrogen,  and  are  nearly  iden- 
tical in  their  composition  with  the  fixed  vegetable  oils;  the  same  ultimate 
principles,  carbon,  hydrogen,  and  oxygen  being  the  constituents  of  both. 
They  also  answer  equally  well  for  the  purpose  of  giving  light,  the  manufac- 
ture of  soap,  and  the  other  uses  to  which  such  substances  are  applied(25). 

Emily.  But,  Mrs  B.,  there  must  be  some  great  difference  between  the 
composition  of  oils,  and  such  fats  as  suet;  the  former  are  fluids,  and  the 
latter  solids. 

Mrs  B.  The  fixed  oils  and  fats  are  not  pure  proximate  principles,  but 
consist  of  two  distinct  substances,  one  of  which  at  common  temperatures  is 
solid,  whilst  the  other  is  fluid.  The  former  is  called  STEAIHSTE,  the  latter 
ELAiSE(26).  The  more  solid  fats,  such  as  suet,  consist  principally  of  stea- 
1'ine,  whilst  the  more  fluid  of  the  oils  are  almost  wholly  elaine.  Those 
which  are  intermediate  in  consistency,  are  so  in  consequence  of  the  propor- 
tionate quantity  of  these  principles  contained  in  them(27). 

Emily.  That  accounts  very  satisfactorily  indeed  for  the  different  degrees 
of  hardness  in  these  substances,  but  you  have  intimated  that  the  oils  and 
fats,  if  not  actually  acids,  are  capable  of  becoming  such. 

Mrs  B.  It  has  been  discovered  that  when  these  fatty  matters  are  com- 
bined with  alkalies  to  form  soap,  a  new  arrangement  of  their  elements  takes 
place,  two  acids  being  formed,  one  of  which  is  called  margaric  and  the 
other  oleic  acid:  both  of  these  combine  with  the  alkali,  and  thus  produce 
soap(28).  During  the  process,  a  third  principle  is  separated  from  them, 
•which  has  received  the  name  of  glycerine.  This  is  a  transparent  liquid, 
which  is  inflammable,  has  neither  taste  or  odour,  and,  unlike  the  oils,  is 
soluble  in  water(29). 

Caroline.  The  margarie  and  oleic  acids,  you  have  told  us,  exist  in  com- 
bination with  the  alkali,  when  soap  is  formed;  but  still  they  must  be  sepa- 
rable from  each  other,  or  their  distinct  natures  6ould  not  have  been  known. 

Mrs  B.  Soap  made  with  potash  may  be  considered  as  an  oleate  and  mar- 
garate  of  that  alkali:  these  acids  can  be  separated  from  each  other  by  means 
of  alcohol,  one  of  them  being  soluble,  and  the  other  insoluble,  in  that 
fluid(SO).  The  margaric  acid,  when  obtained  alone,  is  a  brilliant, white 
solid,  of  a  pearly  lustre  and  crystalline  texture.  It  has  an  appearance 
somewhat  like  that  of  spermaceti,  but  more  beautiful.  Manufactories  have 
been  established  for  procuring  it  from  lard,  and  excellent  candles  are 
made  from  it(31). 

Oleic  acid  is  a  colourless,  oily  fluid,  which  does  not  congeal  until  its 
temperature  is  reduced  nearly  to  zero.  In  the  conversion  of  suet  into  soap, 


24.  What  animal  substances  is  it  said  assume  the  acid  form? 

25.  What  is  observed  respecting  the  animal  oils  and  fats? 

26.  Of  what  two  principles  do  the  different  oils  and  fats  consist ? 

27.  For  what  circumstance  respecting  them  does  this  account? 

28.  \Vhat  is  observed  respecting  the  formation  of  two  acids? 

29.  What  third  principle  do  the  fats  contain? 

30.  What  is  said  of  the  separability  of  margaric  and  oleic  acids? 

31.  What  are  the  appearance  and  use  of  margaric  acid? 


304  CONVERSATIONS  ON  CHEMISTRY. 

- 

a'third  acid,  called  stearic,  has  also  been  detected;  it  bears  a  strong  resem- 
blance to  the  margaric(32). 

Caroline.  In  the  progress  of  discovery  it  seems  likely  that  the  chemists 
will  make  the  catalogues  of  animal  acids  and  of  the  other  animal  products, 
as  extensive  as  those  of  vegetables. 

Mrs  B.  There  is  reason  to  believe  that  other  acids  are  actually  gene- 
rated from  different  kinds  of  fat,  in  the  process  of  saponificationy  or  con- 
version into  soap;  but  these  are  not  to  be  confounded  with  those  principles 
which  exist  ready  formed  in  the  living  system(33). 

Emily.  I  have  read  of  the  conversion  of  animal  muscle  into  a  substance 
which  has  some  resemblance  to  spermaceti;  a  change  said  to  be  produced 
by  the  influence  of  water. 

Mrs  B.  Such  a  change  does  actually  take  place  when  fresh  muscle  is 
exposed  to  the  action  of  water,  or  of  moist  earth.  The  substance  so  pro- 
duced has  been  called  adipocire(3&).  Chemists,  however,  are  not  agreed 
as  respects  its  nature;  some  think  it  a  real  conversion  of  fibrin  into  adipo- 
cire;  others  contend  that  the  fibrin  is  merely  removed  from  the  fatty  matter 
which  originally  accompanied  it;  and  others,  again,  that  the  substance  ob- 
tained is  a  species  of  soap,  containing  a  considerable  portion  of  margarie 
acid(55). 

Caroline.  As  some  of  the  proximate  principles  contained  in  vegetables, 
are  capable  of  being  transformed  into  others  of  the  same  class,  there  appears 
no  good  reason  to  conclude  that  the  same  may  not  be  the  case  to  a  much 
greater  extent  than  is  now  known.  Why  may  not  oils  and  fats,  therefore, 
be  produced  by  a  new  arrangement  of  the  particles  of  those  substances 
which  contain  their  constituents? 

Jlfrs  B.  Thus  to., produce  them  is  certainly  not  beyond  the  probable 
triumph  of  the  chemical  arts;  indeed  it  appears  that  substances  resembling 
oil  have  actually  been  generated  by  causing  the  bases  of  certain  gases  which 
contain  its  constituents,  to  combine  together(36). 

Berard,  a  French  chemist,  mixed  together  carbonic  acid,  hydrogen,  and 
carburetted  hydrogen,  which  he  passed  through  a  red  hot  tube,  and  obtained 
a  white  crystalline  substance,  having  the  general  properties  of  spermaceti. 
In  the  hands  of  another  chemist  a  similar  result  followed  from  a  mixture  of 
coal  gas,  and  aqueous  vapour(37). 

Emily.  Both  stearine  and  elaine  must  enter  into  the  composition  of 
milk,  as  we  are  furnished  with  butter  from  the  cream  contained  in  it.  There 
must,  however,  be  several  other  principles  besides  these  in  this  liquid. 

Jlfrs  B.  MILK,  as  it  was  designed  by  the  great  Author  of  our  existence 
to  be,  for  awhile,  the  sole  nourishment  of  animal  nurslings,  consists  of 
those  ingredients  which  are  most  easily  digested  and  assimilated.  Its  most 
abundant  principles  are  cream,  caseous  matter  or  curd,  and  wAez/(38).  In 
these  are  also  contained  a  saccharine  substance,  called  sugar  of  milk;  mu- 
riate and  phosphate  of  potassa;  phosphate  of  lime;  acetic  acid;  acetate  of  po- 
tassa;  and  a  trace  of  acetate  of  iron.  All  the  substances,  therefore,  which 
are  required  to  form  the  solid  and  the  fluid  parts  of  the  growing  animal,  are 
contained  in  this  single  fluid(39). 

Caroline.     The  three  principal  constituents  of  milk  appear  to  be  very 


32.  What  of  oleic  acid,  and  what  is  said  of  stearic  acid? 

33.  What  general  remarks  are  made  respecting  such  acids? 

34.  In  what  way  is  the  substance  called  adipocire  formed? 

35.  What  different  opinions  have  been  entertained  respecting  it? 

36.  What  is  observed  on  the  possibility  of  forming  certain  bodies? 

37.  What  examples  are  given  of  the  forming  of  oils? 

38.  What  are  the  principal  substances  in  milk? 

39.  What  other  articles  have  been  detected  in  this  fluid* 


ON  MILK.  305 

loosely  combined;  as  the  cream  rises  spontaneously  to  the  surface,  and  the 
curd  and  whey  will  afterwards  separate  from  each  other  if  the  milk  is 
allowed  to  become  sour,  or  if  a  little  rennet  is  poured  into  it(40). 

Mrs  B.  Such  is  the  fact:  this  separation,  however,  is  by  no  means  a  per- 
fect one.  When  the  cream  rises,  it  carries  with  it  a  portion  of  the  caseous 
matter  and  of  the  whey,  which,  in  the  process  of  churning,  separate  in  the 
form  of  buttermilk(41).  The  curd  also  retains  a  small  portion  of  the  cream. 
When  milk  is  intended  to  be  made  into  cheese,  no  part  of  the  cream  should 
be  separated.  Good  cheese  is,  consequently,  rarely  produced  in  those 
dairies  where  much  butter  is  made;  the  former  being  robbed  for  the  sake  of 
the  latter(42). 

Caroline.  What  is  rennet,  and  how  does  it  operate  in  causing  the  curd 
to  separate  from  the  whey? 

Mrs  B.  Rennet  is  made  by  infusing  in  hot  water  the  inner  coat  of  the 
stomach  of  a  calf:  its  peculiar  property  is  derived  from  the  gastric  juice,  of 
•which  we  shall  speak  hereafter(43).  Either  rennet,  or  acids,  will  produce 
the  coagulation  of  the  curd,  but  their  mode  of  operation  is  not  well  under- 
stood. When  this  coagulation  is  effected  in  new  milk,  the  cream  is  en- 
tangled with  the  caseous  matter,  and  a  rich  cheese  may  be  made  from  it; 
but  the  curd,  alone,  produces  a  cheese  which  is  altogether  unfit  to  be  used  as 
an  article  of  food(44). 

Emily.     Curd,  then,  as  usually  obtained,  is  not  pure  caseous  matter. 
Mrs  B.      By  no  means.      To  procure  pure   caseous  matter,  it  must  be 
obtained  from  skimmed  milk,  and  be  well  washed  with  water.     It  is  then 
white,  insipid,  and  inodorous,  and  bears  a  considerable  resemblance  to  albu- 
men, although  it  is  by  no  means  the  same  substance(45). 

Caroline.  The  organs  of  digestion  and  secretion  may  well  prepare  and 
appropriate  the  various  substances  required  for  the  nourishment  of  the  sys- 
tem- from  an  article  so  well  adapted  to  this  purpose  as  milk.  But  it  ap- 
pears really  surprising  that  the  delicate  machinery  intended  for  these  pur- 
poses is  not  totally  deranged  and  destroyed  by  the  various  heterogeneous 
and  indigestible  compounds  with  which  luxury  and  fashion  inauce  us  to 
pamper  our  appetite. 

Mrs  B.  The  process  of  digestion;  some  inquiries  into  the  nature  of  the 
blood;  the  operation  of  respiration,  and  the  production  of  animal  heat,  will 
form  the  principal  topics  of  our  next,  and  last,  conversation.  I,  however, 
shall  then  direct  your  attention  to  some  other  particulars  which  have  hitherto 
been  but  slightly  noticed. 


40.  What  proves  that  the  cream,  whey,  and  curd,  are  loosely  combined? 

41.  Does  this  separation  appear  to  be  a  perfect  one? 

42.  What  is  remarked  respecting  the  making  of  good  cheese? 

43.  How  is  the  rennet  obtained  which  is  used  for  coagulating  milk? 
44  What  further  remarks  are  made  on  the  coagulation  of  milk? 
45.  How  may  pure  caseous  matter,  or  curd,  be  procured^ 


2  A  2 


306  CONVERSATIONS  ON  CHEMISTRY. 


CONVERSATION  XXXI. 

ON  DIGESTION,  SECRETION,  ANIMAL  HEAT,  &c. 

Formation  of  Chyme  and  Chyle.  Bile,  its  Secretion  and  Use.  The  Gas- 
tric Juice.  Its  remarkable  Solvent  Power.  Circulation  of  the  Blood.  Ar- 
terial and  Venous  Blood.  Change  produced  in  the  Blood  by  Respiration. 
Priestley's  Experiments  on  the  Effects  of  Oxygen  on  Venous  Blood.  Per- 
meability of  Membranes.  Carbonic  Acid  exhaled  from  the  Lungs.  Animal 
Heat  influenced  by  Respiration.  Conclusion. 

Mrs  B..  We  are  to  commence  to-day  with  the  PROCESS  or  DIGESTION, 
which  is,  necessarily,  the  first  step  towards  nutrition.  This  process  is  per- 
formed in  the  stomach,  and  is  effected  principally  by  the  agency  of  the  gastric 
juice,  a  fluid  secreted  in  that  organ.  Other  fluids,  which  are  supplied  from 
other  sources,  however,  lend  their  aid  in  carrying  on  this  operation(l). 

The  food  is  intimately  mixed  in  the  stomach  with  these  juices,  is  dissolved 
and  converted  into  a  semi-fluid,  pulpy  mass,  which  is  denominated  CHYME. 
It  is  from  this  mass  that  the  absorbent  vessels,  called  the  lacteals,  select  those 
particles  which  are  destined  to  nourish  the  whole  system(2). 

Caroline.  And  how  do  these  lacteal  vessels  operate  in  making  this  se- 
lection? 

Mrs  B-  That  is  a  question  which  I  cannot  answer,  and  for  reasons 
which  on  a  moment's  reflection  must  be  apparent  to  you.  We  know  how- 
ever that  after  the  chyme  has  been  prepared  by  the  gastric  juice,  these  lac- 
teal absorbents,  which  are  situated  in  that  part  of  the  intestinal  canal  which 
the  chyme  first  enters,  obtain  from  it  a  white  opake  fluid,  to  which  the  name 
of  chyle  has  been  appropriated(S). 

CHYLE,  when  fresh,  possesses  an  appearance  much  resembling  milk.  Its 
taste  is  sweetish,  and  at  the  same  time  somewhat  saline.  After  exposure 
for  a  few  minutes  to  the  air,  it  coagulates,  and  eventually  separates  into  a 
solid  mass,  and  a  limpid  fluid  much  like  the  serum  of  the  blood(4). 

Emily.  This  chyle  must,  of  course,  like  milk,  contain  all  the  ingredients 
necessary  to  the  nourishment  of  the  body;  but  in  what  way  do  the  lacteals 
dispose  of  it? 

Mrs  B.  It  is  conveyed  by  them  into  a  tube  which  is  named  the  thoracic 
duct;  and  by  this  it  is  carried  into  a  large  vein,  called  the  subclavian  vein, 
where  it  mixes  with  the  blood,  and  is  itself  soon  converted  into  that  fluid(5). 
It  is  from  the  blood,  that  all  the  materials  are  supplied  which  support  the 
growth,  or  supply  the  waste,  of  the  system  in  all  its  parts,  whether  fluid  or 
solid(6). 

Emily.  How  numerous  must  be  the  absorbent  vessels,  and  how  various 
and  distinct  their  offices!  Well  indeed  might  David  say  that  "  we  are  fear- 
fully and  wonderfully  made."  Are  these  various  secretions  to  be  attributed 
to  chemical  affinity,  or  to  some  mysterious  mechanical  filtration? 

Mrs  B.  In  many  parts  of  the  body,  numbers  of  small  vessels  are  col- 
eeted  together  in  little  bundles,  which  are  called  glands,  from  a  Latin  word, 


1.  What  is  observed  respecting  the  process  of  digestion? 

2.  What  is  the  first  change  produced  in  the  food? 

3.  What  is  the  office  of  the  lacteals,  and  how  are  they  situated? 

4.  What  are  the  characteristics  of  the  fluid  called  chyle? 

5.  How  is  the  chyle  conveyed,  and  into  what  is  it  converted? 

6.  From  what  does  the  system  derive  its  nutriment? 


ON  BILE  AND  THE  GASTRIC  JUICE.  307 

meaning  an  acorn,  as  some  of  them  are  thought  to  resemble  that  fruit  in  their 
form.  The  office  of  the  glands  is  to  secrete,  or  separate,  certain  matters 
from  the  blood(7). 

The  animal  principles  are  not  separated  from  the  blood  by  mere  mechan- 
ical filtration,  but  are  chemically  produced.  The  substances  thus  formed 
are  not  contained  in  the  blood,  although  their  constituents  exist  in  that  fluid. 
The  secretions  are  of  two  kinds;  those  which  consist  of  peculiar  animal  fluids, 
as  bile,  tears,  saliva,  &c. ;  and  those  which  form  the  general  materials  of 
the  animal  system,  for  the  purpose  of  recruiting  and  nourishing  the  several 
organs  of  the  body;  such  as  albumen,  gelatine,  and  fibrin:  the  latter  have 
sometimes  been  distinguished  by  the  name  of  nutritive  secretions(8). 

Caroline.     I  am  quite  astonished  to  hear  that  all  the  secretions  should  be 
derived  from  the  blood.     I  thought  that  the  bile  was  produced  by  the  liver. 
Mrs  B.     So  it  is;  but  the  liver  is  nothing  more  than  a  very  large  gland, 
•which  secretes  the  bile  from  the  blood(9). 

Caroline.  Bile  must  answer  some  useful  purpose,  or  so  large  a  gland 
would  not  be  provided  for  its  secretion;  yet  it  appears  to  be  a  frequent  cause 
of  disease.  This,  I  suppose,  arises  from  its  excess. 

Mrs  B.  With  the  uses  of  BILE,  we  are  not  very  well  acquainted;  but  it 
appears  to  act  an  essential  part  in  the  conversion  of  chyme  into  chyle,  and 
to  operate  as  a  general  stimulus  to  the  intestinal  canal.  When  the  secre- 
tion of  bile  is  arrested,  or  its  passage  into  the  intestines  obstructed,  those 
diseases  are  produced  which  fully  indicate  the  importance  of  this  fluid  to 
our  well  being(lO). 

Caroline.  The  gastric  juice,  which  is  contained  in  the  stomach,  and 
of  which  you  have  spoken  as  the  main  agent  in  producing  the  solution  of  the 
food,  is  one  of  which  we  are  anxious  to  learn  something  further.  This  fluid 
must  be  a  most  powerful  solvent. 

Mrs  B.  The  sensible  properties  of  the  GASTKIC  JUICE,  would  never 
have  led  us  to  the  inference  that  it  possessed  any  extraordinary  solvent 
power.  When  obtained  from  the  stomach,  it  is  a  transparent  fluid,  the 
taste  of  which  is  slightly  saline,  without  any  indication  of  the  possession 
either  of  acid  or  alkaline  properties.  During  the  period  when  the  process 
of  digestion  is  going  on,  however,  free  muriatic  acid  may  be  detected  in 
it(ll). 

Emily.  It  appears  most  astonishing  that  such  a  fluid  should  act  with  the 
power  it  does  upon  solid  animal  and  vegetable  matter;  but  may  it  not,  in 
fact,  be  greatly  aided  by  some  mechanical  action  of  the  stomach  itself? 

Mrs  B.  Although  the  gastric  juice  is,  in  appearance,  as  simple  a  fluid  as 
saliva,  its  solvent  power  is  a  fact  most  satisfactorily  established.  Meat,  and 
other  alimentary  substances,  mixed  with  it  and  kept  at  about  the  tempera- 
ture of  the  body,  are  entirely  dissolved  by  it.  To  prove  that  in  the  living 
animal,  the  solution  of  the  food  is  altogether  a  chemical  process,  such  sub- 
stances as  are  usually  eaten  have  been  enclosed  in  tubes  or  balls  of  silver, 
perforated  with  holes:  these  have  been  swallowed,  and  the  contained  ma- 
terials have  been  as  completely  acted  upon,  as  when  eaten  in  the  usual 
\ray(12).  The  gastric  juice  is  powerfully  antiseptic;  not  only  preserving 
flesh  which  is  immersed  in  it,  but  actually  removing  the  taint  from  that  in 
which  putrefaction  had  commenced(13). 


7.  What  is  said  of  the  glands  and  their  office? 

8.  What  remarks  are  made  on  their  mechanical  and  chemical  action? 

9.  What  is  the  liver,  and  what  fluid  is  secreted  by  it? 

10.  What  is  said  respecting  the  uses  of  the  bile? 

11.  What  is  first  remarked  respecting  the  gastric  juice? 

12.  What  proof  is  given  of  its  extraordinary  solvent  power? 

13.  What  other  remarkable  property  is  possessed  by  it? 


308  CONVERSATIONS  ON  CHEMISTRY. 

Caroline.  An  alchemist,  who  boasted  that  he  had  discovered  the  uni- 
versal solvent,  was  asked  in  what  vessel  he  could  keep  it.  May  we  not 
with  equal  propriety  inquire  how  this  universal  solvent  of  animal  substances 
can  be  contained  in  the  stomach,  which  is  itself  an  animal  organ(l4)> 

Mrs  B.  This  circumstance  affords  one  of  the  most  remarkable  eviden- 
ces of  the  controlling  power  of  the  living  principle,  which,  during  the 
existence  of  the  animal  enables  it  to  resist  the  operation  of  this  active  agent 
upon  the  coats  of  the  stomach.  It  is  a  fact,  which  has  been  well  ascertain- 
ed, that,  after  death,  the  gastric -juice  begins  immediately  to  operate  upou 
this  organ,  and  dissolves  it  as  it  would  other  animal  matter(15). 

Emily.  With  all  his  acquirements  and  discoveries,  how  limited  is  the 
power  of  man !  How  perpetually  he  fails  even  in  the  attempt  to  imitate  s.ome 
of  those  compounds  with  the  constitution  of  which  he  has  become  familiarly 
acquainted!  Yet,  by  the  hand  of  nature  they  appear  to  be  formed  almost 
without  an  effort. 

Mrs  J3.  We  have  traced  the  nutritious  part  of  our  food  through  the 
lacteals  into  the  thoracic  duct,  and  thence  into  a  vein  called  the  subclavian, 
in  which  it  mixes  with  the  general  mass  of  the  blood(l6).  '  Neither  the  time 
which  we  have  to  devote  to  the  inquiry,  nor  the  state  of  your  anatomical 
knowledge,  will  admit  of  a  very  minute  examination  of  the  circumstances 
connected  with  the  passage  of  this  fluid  through  the  veins  and  arteries;  nor 
indeed  does  this  inquiry  properly  belong  to  the  province  of  the  chemist. 
.  You  have  frequently  heard  of  the  CIRCULATION  OF  THE  BLOOD;  tell  me, 
Caroline,  in  what  you  understand  this  process  to  consist. 

Caroline.  The  idea  that  I  have  of  the  circulation  of  the  blood,  is,  that  it 
runs  from  the  heart  as  its  fountain,  through  all  the  veins  of  the  body,  and  is 
by  them  carried  back  again  to  the  heart.  I  do  not  pretend,  however,  to  any 
knowledge  upon  this  subject,  as  it  is  one  into  which  I  have  never  inquired. 

Emily.  There  must  be  something  more  in  the  circulation  than  you 
mention,  as  the  blood  runs  through  arteries,  as  well  as  through  veins,  and 
although,  like  yourself,  I  have  but  little  information  concerning  anatomy, 
yet  I  know  that  there  is  a  difference  between  the  blood  in  the  arteries,  and 
that  in  the  veins. 

f  Mrs  B.  The  heart  is  a  strong  muscular  bag,  possessing  the  power  of 
alternately  expanding  and  contracting,  by  which  operation  it  first  receives 
the  venous  blood  into  its  cavities,  and  then  forces  it  out  again,  in  order  to 
keep  up  its  circulation.  The  arteries  are  vessels  which  receive  the  blood 
directly  from  the  heart,  and  convey  it  to  all  the  extremities  of  the  body. 
Those  into  which  the  blood  is  forced,  are  large,  but  they  form  numerous 
branches  in  their  course,  and  terminate  in  a  countless  number  of  extremely 
minute  tubes.  From  these,  the  blood  is  received  by  the  veins,  which  con- 
duct it  back  again  to  the  heart(17). 

Caroline.  Pray  in  what  respect  does  the  blood  differ  in  these  two  sets  of 
Vessels,  -which  appear  so  similar,  and  so  evidently  contribute  to  the 
same  end? 

Mrs  B.  Whilst  circulating  through  the  arteries,  the  blood  is  of  a  florid 
red  colour,  but  in  the  veins  its  hue  is  that  of  a  very  dark  purple.  You 
are  already  informed  that  the  different  glands  secrete  the  solids  and  fluids 
which  are  required  for  the  support  and  supply  of  the  whole  system.  These 
secretions  are  all  effected  during  the  passage  of  the  blood  through  the  arte- 
ries, and  it  is  thus  deprived  of  a  large  portion  of  those  principles  which  are 
necessary  to  the  carrying  on  of  the  animal  functions.  This  reduces  it  to  the 

_ . 

14.  What  question  is  asked  respecting  the  gastric  juice? 

15.  What  observations  are  made  in  reply  to  this  question? 

16.  Repeat  what  has  been  said  on  the  first  formation  of  the  blood. 

17.  In  what  way  is  the  circulation  of  the  blood  carried  on? 


ON  THE  BLOOD.  309 

state  in  which  it  exists  in  the  veins,  through  which  it  is  returned  to  have  its 
power  renewed(18). 

Caroline.  This  renewal,  I  suppose,  is  principally  effected  by  the  fresh 
supply  which  it  receives  from  the  thoracic  duct;  but  that  does  not  appear  to 
me  to  account  in  the  least  for  the  great  change  which  takes  place  in.  its 
colour. 

Mrs  JB.  The  change  in  the  colour  of  the  blood  is  produced  in  the  act 
of  respiration,  of  which  I  shall  speak  presently,  but  I  will  firs.t  give  you 
some  information  respecting  the  composition  of  this  vital  fluid(19). 

BLOOD,  when  first  drawn,  appears  to  the  naked  eye  to  be  a  homogene- 
ous fluid;  but  if  examined  by  the  microscope,  it  is  seen  to  consist  of  nu- 
merous little  red  globules,  floating  in  a  colourless  liquid.  In  a  short  space 
of  time  its  compound  nature  is  rendered  perfectly  visible,  as  it  soon  sepa- 
rates into  two  distinct  parts;  one,  a  yellowish  transparent  fluid,  called  the 
serum;  the  other,  a  red  mass,  known  by  the  name  of  the  clot,  or  crassa- 


Emily.  You  spoke  of  the  serum  in  our  last  conversation,  and  mentioned 
its  containing  a  large  quantity  of  albumen.  From  the  abundance  of  this 
principle,  it  will,  of  course,  become  solid,  if  considerably  heated. 

J\frs  _B.  I  noticed  the  use  of  albumen  in  clarifying  different  liquids.  In 
consequence  of  its  containing  so  much  of  this  principle,  the  serum  from  the 
blood  of  animals  has  been  extensively  employed  in  the  refining  of  sugar. 
The  chemist,  however,  has  discovered  modes  of  completing  this  process  . 
without  the  use  of  serum,  and  there  are  now  many  manufactories  in  which 
it  is  altogether  rejected(21). 

Caroline.     I  am  very  glad  of  that,  for  the  idea  of  the  use  of  blood  in 

the  making  of  loaf  sugar,  was  never  one  of  the  most  agreeable  associations. 

Mrs  JB.     Besides  albumen,  the  serum  contains  water,  salts  of  soda  and 

potassa,  some  earthy  phosphates,  and  other  ingredients.     The  muriatic  salts 

are  sufficient  in  quantity  to  communicate  to  it  a  sensibly  saline  taste(22). 

The  crassamentum,  or  clot,  is  more  completely  animalized  than  the 
serum,  Us  principal  constituent  being  fibrin,  which  is  identical  in  its  com- 
position with  that  which  constitutes  the  basis  of  the  muscles.  The  colouring 
inatter  may  be  washed  out  from  the  red  clot,  and  the  fibrin  obtained  in  a 
separate  state(23). 

Emily.  Upon  what  particular  substance  does  the  red  colour  of  the  blood 
appear  to  depend. 

Mrs  JB.  This  is  a  point  which  has  been  much  disputed,"  and  cannot  yet 
be  considered  as  well  settled.  It  is  believed,  however,  to  result,  principally, 
from  the  presence  of  iron,  The  existence  of  this  substance  in  the  colouring 
matter  of  the  blood,  was  long  ago  detected;  and  the  fact  has  been  confirmed 
by  recent  experiments.  Its  quantity  is  minute,  but  as  it  is  contained  in  the 
colouring  matter  only,  the  inference  appears  to  be  a  fair  one,  that  it  is 
essentially  the  colouring  ingredient(24). 

Caroline.  As  the  bones  consist  of  phosphate  of  lime,  I  should-  have 
looked  for  the  presence  of  this  earth  in  the  blood;  for  otherwise  the  secreting 
vessels  which  are  destined  to  nourish  those  solid  pillars  of  the  body,  could 
not  obtain  their  supply.  But  although  the  poets  have  imagined  that  there 
might  be  a  flow  of  "  iron  tears  down  Pluto's  cheeks,"  I  never  expected  to 


18.  What  is  observed  respecting  arterial  and  venous  blood? 

19.  In  what  operation  of  the  system  is  the  change  in  its  colour  produced? 
iJO.  What  is  said  of  the  first  appearance  and  the  separation  of  blood? 

21.  What  is  observed  of  the  use  of  scrum  in  refining  sugar? 

22.  What  substances  are  enumerated  as  contained  in  the  blood? 

23.  What  is  said  respecting  the  crassamentum,  or  clot? 

S4.  Upon  what  substance  does  the  colour  of  the  blood  appear  tq  depend? 


310  CONVERSATIONS  ON   CHEMISTRY. 

learn  the  philosophical  truth  that  a  current  of  iron  was  actually  coursing  its 
way  through  every  part  of  the  body. 

Emily.  By  what  particular  operation  of  the  system  is  the  venous,  changed 
into  arterial  blood  ?  The  transformation  appears  to  be  performed  with  great 
rapidity,  as  it  arrives  at  the  heart  in  the  former  state,  and  leaves  it  in  the 
latter. 

Mrs  J3.  The  process  of  RESPIRATION  will  lend  us  some  aid  in  account- 
ing for  this  change,  as  it  appears  evidently  to  take  place  in  the  lungs.  Af- 
ter the  blood  has  performed  its  function  of  nourishing  the  body,  it  is  returned 
into  one  of  the  cavities  of  the  heart,  called  its  right  ventricle:  this,  by  its  mus- 
cular power,  contracts,  and  throws  the  fluid  through  a  large  vessel  into  the 
lungs,  which  are  contiguous.  It  circulates  through  this  organ  by  means  of 
vessels  inconceivably  numerous,  and  of  a  very  delicate  texture,  where  it  is 
exposed  to  the  action  of  the  air  which  is  inhaled  at  every  breath.  The 
oxygen  of  the  air  acts  upon  the  blood,  in  a  way  that  deprives  it  of  its  dark 
colour,  and  gives  to  it  the  florid  hue,  and  other  properties  which  it  poss- 
esses in  the  arteries(25). 

Caroline.  But  how  is  this  possible?  Whilst  the  air  and  the  blood  are 
completely  separated  from  each  other  by  a  membrane,  they  cannot  possibly 
come  into  contact  with  each  other(26). 

Mrs  B.  Your  objection  is  one  which  any,  person  unacquainted  with  the 
facts  of  the  case  might  fairly  urge.  Dr  Priestley  first  observed  that  the  red 
colour  which  is  so  soon  produced  upon  the  surface  of  the  blood  drawn  from 
the  veins,  resulted  from  the  action  of  the  oxygen  contained  in  the  atmos- 
phere; and  he  ascertained  that  when  kept  from  contact  with  this  gas,  it  re- 
tained its  dark  colour.  Upon  enclosing  a  portion  of  blood  in  a  bladder,  he 
found  that  the  same  change  was  effected,  notwithstanding  the  intervention 
of  the  membrane  between  the  fluid,  and  the  oxygen  of  the  air(27). 

Emily.  That  is  a  very  extraordinary  circumstance.  If  air  can  pass 
through  bladders,  how  can  hydrogen  or  other  gases  be  retained  in  them  in  a 
state  of  purity  for  chemical  experiments? 

Mrs  B.  This  in  fact  cannot  be  done.  If  a  bladder  is  inflated  by  hydro- 
gen, a  double  process  immediately  commences;  a  portion  of  this  gas  passes 
ithrougii^aTn}  escapes,  whilst  its  place  is  supplied  by  the  passage  of  atmos- 
pheric air  inwards.  The  bladder,  therefore,  will  still  remain  full,  but  it  will 
soon  contain  a  mixture  of  hydrogen  and  atmospheric  air.  Carbonic  acid, 
and  other  gases  penetrate  sirch  membranes  with  considerable  facility,  one  air 
passing  out  and  another  in.  The  gases  pass  through  with  different  degrees 
of  facility;  and  it  is  a  fact  that  a  bladder  partially  filled  with  one  kind  of  air, 
and  exposed  on  its  outside  to  a  gas  more  penetrative  than  the  former,  will 
become  completely  inflated,  and,  if  not  very  strong,  will  burst  spontane- 
ously^). 

Caroline.  My  objection  is  indeed  answered  in  a  very  satisfactory  man- 
ner, and  a  most  remarkable  fact  at  the  same  time  made  known  to  us,  which 
but  for  the  evidence  of  experiment  could  scarcely  obtain  credence. 

Mrs  B.  This  penetrability  of  membranes  is  intimately  connected  with 
the  effects  of  respiration.  We  inhale  atmospheric  air,  and  when  this  is 
discharged  from  the  lungs,  it  contains  about  one-twelfth  part  of  carbonic 
acid.  A  portion  of  the  oxygen  of  the  air  has  disappeared,  and  is  replaced 
by  a  corresponding  portion  of  fixed  air.  As  this  occurs,  the  venous  is 



25.  What  further  is  said  of  its  circulation  and  change  of  colour? 

26.  What  objection  is  urged  against  the  action  of  the  air  on  the  blood? 

27.  In  what  way  is  this  objection  obviated? 

28.  What  information  is  given  respecting  the  penetrativeness  of  mem 
branes  by  gases? 


ON  ANIMAL  HEAT.  311 

changed  into  arterial  blood(29).  It  appears  therefore  that  the  dark  hue  of 
the  former  arises  from  its  containing- a  quantity  of  carbon,  which,  combining 
•with  the  oxygen  of  the  air,  becomes  carbonic  acid,  and  is  thus  expelled  with 
the  breath.  The  blood,  relieved  from  its  superabundance  of  carbon,  as- 
sumes a  florid  hue,  and  becomes  arterial(SO). 

Emily.  This  theory  of  respiration  is  to  me  equally  gratifying  and  novel. 
I  most  sincerely  regret  that  my  want  of  anatomical  knowledge  interferes 
with  that  full  comprehension  of  the  subject  to  which  an  intimate  acquaint- 
ance with  the  animal  structure  is  manifestly  necessary. 

•Mrs  B.  When  the  blood  has  been  thus  arterialized  in  the  lungs,  it  is 
collected  into  vessels  which  convey  it  into  the  left  ventricle  of  the  heart. 
Thence  it  is  propelled  through  all  the  different  parts  of  the  body;  the  large 
artery  which  first  receives  it,  ramifying,  as  I  have  already  told  you, 
throughout  the  whole  frame(31 ). 

Caroline.  But  whence  proceeds  the  carbon  with  which  the  venousblood 
becomes  loaded  ?  I  do  not  perceive  that  the  theory,  in  any  way,  accounts  for 
its  presence. 

Mrs  B.  Carbon  exists  in  greater  quantity  in  the  blood,  than  it  does  hi 
the  organized  parts  of  the  system.  The  arterial  blood,  as  it  supplies  the 
various  secretions,  parts  with  a  larger  proportionate  quantity  of  its  other 
constituents,  than  it  does  of  its  carbon.  It  is*in  consequence  of  its  own  de- 
composition, therefore,  and  not  from  its  acquiring  any  carbon  as  it  passes 
through  the  arteries,  that  the  blood  becomes  loaded  with  it(32). 

Emily.  Were  it  not  for  the  perpetuity  of  >the  operation,  the  small  quan- 
tity of  carbon  given  out  with  the  breath  would  seem  to  be  inadequate  to  the 
decarbonization  of  the  blood. 

J\frs  B.  The  quantity  which  escapes  in  this  way  is  really  very  large. 
It  has  been  calculated  that  the  carbonic  acid  which  is  expelled  from  the 
lungs  in  the  course  of  twenty-four  hours,  actually  contains  eleven  ounces 
of  solid  carbon;  but  from  an  estimation  of  the  quantity  contained  in  our  ordi- 
nary food,  it  would  scarcely  seem  possible  that  such  a  portion  can  be  ex- 
haled with  the  breath(33). 

Caroline.  This  combination  of  oxygen  with  carbon,  and  the  consequent 
production  of  carbonic  acid,  render  the  process  of  respiration  very  similar 
to  that  of  combustion;  a  process  which  would  be  attended  with  some  incon- 
venience were  it  really  to  take  place  in  the  lungs(34j. 

Jtfrs  B.  The  analogy  of  which  you  speak  does  certainly  exist,  and  the 
theory  of  the  production  of  ANIMAL  HEAT,  which  has  been  most  generally  ad- 
mitted as  true  by  the  chemist,  has  its  foundation  in  the  existence  of  such  a 
process(35). 

C.aroline.  But  if  animal  heat  were  kept  up  from  this  cause,  I  should  look 
for  a  corresponding  portion  of  light  to  be  disengaged;  besides,  would  not 
the  lungs  be  hotter  than  any  other  part  of  the  body? 

Jlfrs  B.  When  the  combination  of  oxygen  and  carbon  takes  place  so 
slowly  that  the  heat  disengaged  is  not  intense,  there  is  no  perceptible  light. 
The  advocates  of  this  theory  have  attempted  to  prove  that  the  capacity 
for  heat,  possessed  by  arterial,  considerably  exceeds  that  possessed  by 
venous  blood;  and  that  the  heat  which  is  disengaged  by  the  union  of  the  car- 
bon and  the  oxygen,  goes  to  satisfy  this  increased  capacity,  and  does  not 


29.  What  change  takes  place  in  the  air  which  we  respire? 

SO.  How  does  this  appear  to  operate  in  changing  the  colour  of  the  blood? 

31.  After  it  is  arterialized,  what  then  takes  place? 

32.  In  what  way  does  venous  blood  become  charged  with  carbon? 

33.  What  estimate  has  been  made  of  the  quantity  of  carbon  exhaled? 

34.  What  similarity  exists  between  respiration  and  combustion? 
S5.  How  has  this  been  thought  to  be  connected  with  animal  heat? 


312  CONVERSATIONS  ON  CHEMISTRY. 

therefore,  increase  the  temperature  of  the  lungs.  The  blood,  as  it  supplies 
the  various  secretions  in  every  part  of  the  body,  gradually  returns  to  the 
state  of  venous  blood;  and  as  it  does  so,  the  heat  which  went  to  satisfy  the 
increased  capacity,  becomes  free,  and  is  thus  diffused(36). 

Emily.  This  theory  seems  altogether  to  remove  the  difficulty  which  at 
first  appeared  to  me  insurmountable,  and  applies  the  principles  of  chemittry, 
in  a  very  happy  manner,  to  the  explanation  of  one  of  the  most  interesting 
phenomena  of  the  animal  economy. 

Mrs  B.  You  must  not,  however,  receive  this  theory  as  incontestably 
proved.  Some  eminent  experimenters  have  denied  the  truth  of  the  main 
fact  upon  which  it  is  founded,  and  have  asserted  that  arterial  and  venous 
blood  differ  but  very  little  in  their  capacity  for  heat.  It  has  been  calculated 
also,  that  the  quantity  of  heat  given  out  by  the  body,  very  considerably 
transcends  that  which  would  be  produced  by  the  combination  of  the  carbon 
and  oxygen  in  respiration(37). 

Caroline.  I  am  sorry  that  the  superstructure,  which  I  at  first  thought  so 
beautiful,  stands  upon  a  foundation  so  insecure;  but  perhaps  you  are  pre- 
pared to  account  satisfactorily  for  the  fact  you  mention. 

Mrs  B.  There  has  not  -been  a  theory  proposed  to  account  for  it,  which 
is  not  liable  to  very  strong  objections.  It  is  a  subject  which  the  chemists  and 
physiologists  are  pursuing  with  great  ardour,  and  respecting  which  there  is 
much  to  learn.  That  respiration  and  the  absorption  of  oxygen  are  inti- 
mately concerned  in  the  phenomenon  is  fairly  inferred  from  the  fact  that  the 
heat  in  different  animals  is  proportioned  to  the  quantity  of  oxygen  which 
they  consume.  It  is  certain,  however,  that  other  functions,  such  as  the 
secretions  which  are  going  on  in  every  part  of  the  body,  are  accompanied 
with  a  disengagement  of  heat.  It  is  not  to  chemistry  alone  that  we  are  to 
look  for  an  illustration  of  the  point  in  question;  the  production  of  animal 
heat  is  a  process  of  vitality,  and  probably  will  never  be  perfectly  under- 
stood, as  the  nature  of  life  itself  is  one  of  those  mysteries  which  it  belongs 
to  the  Creator  alone  fully  to  comprehend(38). 

Emily.  The  heat  of  the  blood  is  marked  on  the  thermometer  at  ninety- 
eight  degrees.  Must  not  the  temperature  of  the  body  vary  with  that  of  the 
atmosphere,  with  the  gentleness  or  violence  of  our  exercise,  and  other  cir- 
cumstances? 

Mrs  B.  All  these  circumstances  make  but  little  difference  in  the  tempe- 
rature of  our  bodies,  unless  we  judge  by  the  surface  only.  A  thermometer 
held  in  the  mouth  of  a  person  in  health,  would  scarcely  vary  a  single  degree, 
whether  it  were  tried  in  summer  or  in  winter,  in  the  frigid  or  in  the  torrid 
zone(39). 

Caroline.  But  certainly  when  I  run  fast,  or  otherwise  use  great  exer- 
cise, I  am  warmer  than  at  other  times?  Yet  your  remarks  would  lead  to 
the  conclusion  that  when  I  am  overcome  by  the  sensation  of  heat,  I  am 
really  no  warmer  than  when  shivering  with  cold. 

Mrs  B.  There  is  certainly  a  real  difference  in  you,  in  the  supposed 
cases,  but  the  difference  exists  at  the  surface  only,  and  it  is  by  the  surface 
that  we  judge  of  the  sensation  of  heat.  The  animal  heat  is  generated 
within  the  body  itself,  and  its  equality  is  regulated  by  the  process  of  perspi- 
ration which  is  perpetually  going  on.  Under  ordinary  circumstances  this 
perspiration  is  imperceptible,  yet  the  quantity  of  moisture  which  escapes 
is  considerable.  When  exercise  is  taken  the  perspiration  is  quickened, 
and  if  greatly  increased  becomes  sensible.  In  a  healthy  state  it  is  always 


36.  What  difficulty  is  stated,  and  what  explanation  has  been  given? 

37.  What  remarks  are  made  respecting  this  theory? 

38.  What  further  remarks  are  made  on  the  subject  of  animal  heat? 

39.  What  is  said  respecting  the  temperature  of  the  human  body? 


CONCLUSION.  313 

proportioned  to  the  heat  generated  in  the  body,  and  thus  renders  the  excess 
of  it  latent,  upon  the  same  principle  that  evaporation  from  the  earth  lowers 
its  temperature(40). 

Emily.  What  admirable  resources  has  nature  provided  for  us!  By  the 
production  of  animal  heat,  she  sustains  our  bodies  at  a  temperature  above 
that  of  the  inanimate  substances  by  which  we  are  surrounded;  and  whenever 
its  supply  becomes  too  abundant,  the  excess  is  carried  off  by  perspiration. 

•Mrs  J$.  When  they  are  fairly  examined,  and  correctly  estimated,  we 
shall  find  all  the  operations  of  nature  controlled  and  directed  by  Infinite 
Wisdom  and  Benevolence.  Even  in  the  spontaneous  decay  to  which  every 
thing  that  lives  is  eventually  subjected,  we  may,  instead  of  the  work  of 
final  destruction,  perceive  a  well  ordered  provision;  and  discover  the  means 
by  which  a  perpetual  succession  of  forms,  resplendent  with  beauty,  and  ani- 
mated by  a  spark  from  the  Divinity,  shall  rise  from  the  ashes  of  those  be- 
ings which,  having  fulfilled  the  purposes  of  their  creation,  return  to  the 
elements  from  which  they  were  originally  produced(4l). 


40.  By  what  operation  is  this  temperature  regulated? 

41.  What  are  the  concluding  remarks? 


2  B 


814  GLOSSARY. 


A  GLOSSARY 

vV-1    >i  -'^*»  -41    .".'::.  J'T  .-}'«;'.  .  rj;->(     •  '7 

.  OF  SUCH  TERMS  AS  ARE  NOT   FULLY  EXPLAINED  IN   THE 
BODY  OF  THE  WORK. 

Jleriform.  The  same  as  elastic  fluids.  Having  the  form  of  air.  Those 
which  exist  in  this  form  at  all  common  temperatures  are  called  perma- 
nently elastic  fluids.  Steam  and  other  vapours  are  aeriform  whilst  they 
retain  the  heat  which  converted  them  into  that  state;  but  they  become 
liquids,  or  non-elastic  fluids,  by  a  reduction  of  their  temperature. 
Jllcohol.  The  pure  spirit  obtained,  by  distillation,  from  liquors  which  have 
undergone  the  vinous  fermentation.  This  spirit  when  rectified,  so  as  to 
separate  it  from  the  peculiar  juices  of  the  fermented  liquor,  is  the  same 
from  all.  Alcohol  is  sometimes  called  spirits  of  tvine;  but  what  is  sold 
under  that  name  rarely  deserves  to  be  denominated  alcohol.  What  is 
called  proof  spirit,  contains  nearly  as  much  water  as  alcohol. 
Jlnimal  charcoal.  When  animal  matter  is  submitted  to  destructive  distilla- 
tion, the  black  carbonaceous  matter  which  remains  in  the  retort  is  call- 
ed animal  charcoal.  Bones  are  frequently  so  treated  for  the  purpose 
of  manufacturing  ammonia.  The  residuum,  when  ground,  is  ivory,  or 
bone,  black.  This  is  frequently  called  animal  charcoal;  it  contains,  how- 
ever, the  earthy  matter  of  the  bones,  which  is  phosphate  of  lime. 
Annealing.  Glass,  steel,  and  some  other  substances  become  brittle  if  they 
are  rapidly  cooled  after  being  made  red-hot;  whilst  if  cooled  slowly  this 
brittleness  is  in  a  greater  or  less  degree  prevented.  This  slow  cooling 
is  called  annealing. 

Calcareous.  Lime,  and  those  earthy  minerals  which  contain  a  large  por- 
tion of  lime,  have  received  the  name  of  calcareous  earths. 
Calcination.  Certain  substances  when  changed  by  the  action  of  fire  are  said 
to  be  calcined.  The  name  calx  was  given  to  the  oxide  of  a  metal,  when 
it^was  produced  by  the  action  of  heat.  Lime,  magnesia,  &c.  when  depriv- 
ed by  heat  of  the  water  and  carbonic  acid  with  which  the/  are  usually 
combined,  are  said  to  be  calcined. 

Causticity.     The  pure  alkalies,  the  stronger  acids,  and  some  of  the  metal- 
lic salts,  which  destroy  the  texture  of  the  flesh,  are  said  to  be  caustic. 
Chalybeate.     Containing  iron.     Many  mineral  waters  contain  some  salt  of 

icon,  usually  a  carbonate;  such  waters  are  called  chalybeate  waters. 
Effervescence.  When  gaseous  matter  escapes  rapidly  from  any  mixture, 
so  as  to  occasion  an  appearance  resembling  boiling,  the  liquid  is  said  to 
effervesce.  In  active  fermentations  there  is  an  effervescence;  whenever  a 
stronger  acid  is  poured  upon  an.  alkaline  carbonate,  a  brisk  effervescence 
ensues  from  the  escape  of  carbonic  acid. 

Empyreuma.  That  peculiar  and  very  unpleasant  odour  which  is  produced 
by  heating  vegetable  and  animal  matter  in  close  vessels,  is  called  empy- 
reuma.  If  too  much  heat  be  applied  in  distilling  vegetable  substances, 
a  disagreeable  taste  and  odour  are  acquired  by  the  spirit,  which  are  said 
to  arise  from  empyreumatic  oil. 

Frigoriflc  mixtures.  Those  mixtures  the  materials  of  which  react  upon 
each  other  so  as  to  cause  freezing.  The  cold  produced  results  from 


GLOSSARY. 


315 


the  dissolution  of  solids,  which  in  putting  on  the   fluid  form   absorb 
caloric. 

A  degree  of  cold  much  more  intense  than  that  of  any  known  natural 
temperature,  may  be  produced  by  such  mixtures.  The  following  table 
exhibits  the  power  of  some  of  them. 


Mixtures. 

Thermometer  sinks. 

Degrees  of  cold 
produced. 

Muriate  of  ammonia 
Nitrate  of  potash 
Sulphate  of  soda 
Water 

5  parts"") 

1 

16           J 

From  -f  50°  to  +  4° 

46 

Sulphate  of  soda 
Diluted  nitric  acid 

3  parts  ? 
2           3 

From  -f  50°  to  —  3° 

53 

Snow 
Diluted  sulphuric  acid 

3  parts  ? 
2           3 

From  +  32°  to  —  23° 

55 

Snow                                        2  parts  7 
Muriate  of  lime  crystallized  3            5 

From-f  32°  to  —  50° 

82 

Snow                                       1  part  ? 
Muriate  of  lime  crystallized  3           5 

From  —  40°  to  —  73° 

33 

Snow 
Diluted  sulphuric  acid 

8  parts  7 

10         i 

From  —  68°  to  —  91° 

23 

Gasometer.     An  air  holder,  so  constructed  that  the  quantity  of  gas  which  it 

contains  can  be  ascertained  or  measured. 

Geology.  That  branch  of  science  which  inquires  into  the  structure  of  the 
earth.  The  mineralogist  ascertains  the  nature  of  the  individual  substan- 
ces of  which  the  earth  consists;  whilst  the  geologist  studies  its  architec- 
ture, or  the  general  arrangement  of  the  larger  masses  of  which  it  is 
composed,  and  their  positions  relative  to  each  other. 

Hydrometers.  Instruments  for  ascertaining  the  specific  gravities  of  liquids 
and  other  substances.  These  are  described  in  the  *'  Conversations  on 
Natural  Philosophy." 

Hygrometers.  Instruments  which  indicate  the  relative  quantities  of  mois- 
ture contained  in  the  atmosphere,  in  different  places  and  at  different 
times. 

Hygrometric  moisture.  That  moisture,  or  watery  vapour,  which  is  not  in  a 
state  of  combination,  and  which  will,  therefore,  affect  the  hygrometer  as 
free  caloric  will  affect  the  thermometer. 

Laboratory.  A  place  furnished  with  apparatus  necessary  for  the  per- 
formance of  the  various  operations  in  chemistry. 

Mineralogy.  That  branch  of  science  which  inquires  into  the  nature  of  the 
substances  that  constitute  the  mineral  kingdom.  The  term  mineral  is  de- 
rived from  the  mines  in  which  the  greater  number  of  these  bodies  are 
found;  but  in  its  most  extensive  acceptation  it  includes  all  the  substances 
which  are  inorganic;  or  which,  in  other  words,  do  not  belong  to  the  ani- 
mal or  vegetable  kingdoms.  Those  minerals  which  exhibit  the  forms  of 
organized  matter,  have  received  these  forms  from  such  matter  having  been 
penetrated  by  earthy  or  metallic  substances,  which  the  organized  bodies 
have  thus  moulded  into  their  own  peculiar  shapes.  Such  minerals  are 
termed  fossils,  or  organic  remains. 


316  GLOSSARY. 

/• 

Mineral  -waters.  Spring  water  generally  contains  some  portion  of  earthy, 
saline,  or  other  matter,  derived  from  the  ground  through  which  it  passes. 
When  the  quantity  is  considerable,  and  the  water  is  much  changed  in  its 
sensible  properties,  it  then  becomes  a  mineral  -water. 

Petrifaction.  Animal  and  vegetable  substances  frequently  appear  to  be 
converted  into  stone;  the  external  form  being  retained,  whilst  the  sub- 
stance is  completely  changed.  These  are  called  petrifactions.  Some 
waters  have  the  property  of  effecting  this  change  with  considerable  rapid- 
ity; and  these  are  called  petrifying  waters.  (See  Mineralogy.) 

Phlogiston.  This  name  was  formerly  given  to  a  principle  which  the  older 
chemists  imagined  was  contained  in  all  combustible  substances.  They 
considered  phlogiston  as  the  principle  of  inflammability,  or  the  very  es- 
sence of  light  and  heat.  It  was  thought  that  when  a  combustible  had  been 
burnt,  it  was  deprived  of  its  phlogiston,  or  was  dephlogisticated.  The 
light  and  heat  emitted  in  combustion  were  supposed  to  be  a  consequence 
of  the  separation  of  the  phlogiston  from  the  burning  body;  and  in  order 
to  render  it  again  combustible,  it  was  believed  that  the  phlogiston  must  be 
restored  to  it.  The  metals,  which  we  consider  as  simple  bodies,  were 
regarded  as  combinations  of  phlogiston  with  a  simple  body,  different  for 
each  metal,  called  a  calx,  now  known  to  be  compound,  and  denominated  a 
metallic  oxide.  When  this  calx  was  brought  back  to  the  metallic  state 
by  heating  it  with  charcoal,  it  was  believed  that  the  phlogiston,  with  which 
the  metal  had  parted  in  its  combustion,  was  restored  to  it  by  the  charcoal. 

Pyrophorus.  A  substance  which  takes  fire  by  mere  exposure  to  the  air. 
It  is  made  by  calcining  alum  and  sugar,  or  alum  and  flour  together.  The 
product  must  be  kept  in  a  well  stopped  phial  till  wanted  for  use. 

Quartz.  The  different  kinds  of  minerals  which  consist  almost  exclusively 
of  silex,  are  denominated  quartz.  In  rock  crystal  the  quartz  is  symmet- 
rical in  its  form,  but  it  is  frequently  found  transparent,  without  the  crys- 
talline form.  Many  of  the  minerals  of  this  family  are  opake. 

Radical.  A  term  frequently  used  as  synonymous  with  the  word  basis. 
Sulphur  is  the  radical  of  sulphurous  and  sulphuric  acids.  Carbon  is  the 
radical  of  carbonic  acid. 

Reagents.  Substances  employed  as  tests  to  discover  the  presence  of  any 
particular  ingredient  in  a  substance,  or  compound  to  be  examined.  Gal- 
lic acid  is  employed  as  a  test,  or  reagent,  to  discover  the  presence 
of  iron  in  a  solution;  the  iron  and  the  gallic  acid  react  upon  each  other 
and  produce  a  compound  of  an  intense  blue  colour,  which  serves  to  show 
that  the  metal  in  question  is  contained  in  the  mixture. 

Semi-metal.  This  term  is  now  obsolete,  but  it  was  formerly  applied  to 
those  metals  which  are  most  readily  oxidized,  or  changed,  by  the  action 
of  heat  and  air;  whilst  those  which  most  powerfully  resist  the  influence 
of  the,se  agents,  were  called  perfect  metals. 

Thermometer.  An  instrument  for  measuring,  or  ascertaining,  the  kempera- 
ture  of  bodies.  At  page  47  the  different  kinds  of  thermometers  now 
used  are  described.  Although  Fahrenheit's,  the  Centigrade,  and  Reau- 
mur's scales  are  differently  divided,  they  may  be  readily  compared  with 
each  other  by  observing  the  following  rules. 

Nine  degrees  of  Fahrenheit's  scale  are  equal  to  five  of  the  centigrade, 
and  to  four  of  Reaumur's  thermometer.  Fahrenheit's  is  therefore  reduced 
to  the  centigrade  scale  by  multiplying  by  five,  and  dividing  by  nine;  or 
to  that  of  Reaumur  by  multiplying  by  four,  and  dividing  by  nine.  By 
reversing  the  process  either  of  these  may  be  reduced  to  Fahrenheit  s 
scale.  But  it  must  be  recollected  that  Fahrenheit  has  fixed  the  zero  at 
32  degrees  of  his  scale  below  either  of  the  others,  they  having  their  zero 
at  the  freezing  point.  This  number  32,  must  therefore  be  either  added 
or  subtracted,  as  the  case  may  be,  in  comparing  Fahrenheit  with  either 
of  the  others. 


GLOSSARY.  317 

To  reduce  centigrade  degrees  to  those  of  Fahrenheit,  multiply  by  nine 
and  divide  by  five,  and  to  the  quotient  add  thirty-two. 

To  reduce  Fahrenheit's  to  the  centigrade,  subtract  32,  then  multiply 
the  remainder  by  5,  and  divide  the  product  by  9. 

The  same  rules  answer  for  Reaumur's  and  Fahrenheit's,  substituting 
the  number  4  for  the  number  5,  in  the  foregoing  examples. 
Vitrification.     The  conversion  of  bodies  into  glass,  by   intense  degrees  of 
heat.     The  earths  and  metallic  oxides  generally,  are  capable  of  under- 
going vitrification,  especially  when  mixed  with  each  other. 


2  B  2 


' 


INDEX  TO  THE  EXPERIMENTS.  319 


INDEX 

TO  THE  EXPERIMENTS  DESCRIBED  IN  THIS  WORK. 


Conversation  1. 

1.  Copper  may  be  dissolved  in  sulphuric  acid  by  the  aid  of  nitric  acid, 
and  crystals  of  sulphate  of  copper  obtained  from  the  solution.     See  p.  19. 

2.  If  an  acid  be  dropped  into  a  solution  of  soap,  the  soap  will  be  decom- 
posed.    See  p.  20. 

3.  If  iron  be  put  into  a  solution  of  sulphate  of  copper,  the  iron  will  be 
dissolved,  and  the  copper  precipitated.     See  p.  20. 

4.  If  iron  be  dissolved  in   sulphuric   acid,  crystals  of  sulphate  of  iron 
(copperas)  may  be  obtained  from  the  solution.     See  p.  21. 

Conversation  2. 

5.  The  heat  and  light  from  a  fire  may  be  separated  from  each  other  by 
the  intervention  of  a  pane  of  glass.      See  p.  24. 

6.  The  two  hands  may  be  dipped  together  into  the  same  fluid,  and  the 
sensation  of  cold  experienced  by  one  of  them,  and  that  of  heat  by  the  Other. 
See  p.  32. 

Conversation  3. 

7.  Heat  is  conducted  with  different  degrees  of  celerity  by  the  different 
metals.     See  p.  33. 

8.  Water  may  be  boiled  in  the  upper  part  of  a  vessel,  whilst  ice  remains 
at  the  bottom  of  it.     See  p.  35. 

9.  Ether  burnt  upon  the  surface  of  water  will  not  communicate  heat  to 
that  fluid.     See  p.  36. 

10.  Heat  may  be  reflected  from  polished  metallic  surfaces,  and  concen- 
trated in  the  focus  of  a  mirror.      See  p.  38. 

11.  The  radiation  of  heat  is  greatly  influenced  by  the  kind  of  surface 
possessed  by  the  heated  body.      See  p.   40. 

12.  A  blackened  metallic  vessel  will  be  rapidly  heated  before  a   fire, 
whilst  one  which  is  polished  will  remain  cold  for  a  considerable  length  of 
time.      See  p.  42. 

Conversation  4. 

13.  Bodies  are  expanded  by  being"  heated.     A  metallic  ball  which  when 
cold  exactly  fits  a  brass  ring,  will  not  pass  through  it  when  warmed. 
See  p.  44. 

14.  That  the  different  metals  expand  differently  may  be  shown  by  the 
pyrometer.     Seep.  45. 

15.  Different  fluids  expand  differently  by  the   same  degrees  of  heat. 
See  p.  46. 

16.  That  air  expands  may  be  shown  by  the  air  thermometer.     See  p.  48. 

Conversation  5. 

17.  Water  may  be  boiled  in  a  Florence  flask  over  a  lamp,  and  the  pro 
cess  readily  examined.     See  p.  55. 


320  INDEX  TO  THE  EXPERIMENTS. 

18.  Water  contained  in  a  flask,   and  closely  corked  whilst  boiling,   may 
afterwards  be  made  to  boil  violently  by  the  application  of  ice,  or  of  cold  water. 
See  p.  57. 

19.  Ether  •will  boil  in  an  exhausted  receiver  at  a  temperature  below  the 
freezing-point  of  water,  and  will  convert  water  into  ice.      See  p.  60. 

20.'  The   cold  produced  by  evaporation  may  be  rendered  sensible  by 
dropping  ether  on  the  hand.      See  p.  61. 

21.  Two  liquids  different  in  their  volatility  may  be   separated  by  dis- 
tillation.    See  p.  63. 

Conversation.  6. 

22.  Different  bodies  heated  to  the  same  degree,  contain  different  quanti- 
ties of  caloric  ;   exemplified  by  copper,  lead,  and  tin.     See  p.  68. 

23.  The  quantity  of  heat  which  will  raise  the  temperature  of  a  pound  of 
mercury  28°,  will  elevate  a  pound  of  water  but  1°.     See  p.  69. 

24.  The  rarefaction  of  air  produces  cold.     This  may  be  exhibited  by 
placing  a  thermometer  under  a  receiver  on  the  air  pump,  and  then  exhausting 
the  air  ;  its  condensation  produces  heat.      See  p.  70. 

25.  A  thermometer  placed  in  a  vessel  of  ice  or  snow,  the  temperature  of 
which  is  below  the  freezing  point,  will  rise  to  32°  if  the  vessel  be  exposed 
to  heat ;  but  as  soon  as  the  ice  begins  to  melt,  the  thermometer  will  remain 
stationary.     See  p.  71. 

26.  If  a  pound  of  water  heated  to  172°  be  poured  upon  a  pound  of  ice  at 
32°  the  whole  mixture  will  be  of  the  temperature  of  32°. 

27.  The  heat  which  converts   boiling  water  into  steam,  does  not,  in  the 
slightest  degree,  elevate  its  temperature.      See  p.  73. 

28.  The  steam  produced  contains  a  very  large  quantity  of  heat,  which, 
although  latent  in  the  steam,  may  be  rendered  sensible.     See  p.  73. 

29.  If  common  salt  be  mixed  tvith  ice,  a  reduction  of  temperature  may  be 
produced  amounting  to  about  thirty-two  degrees.     See  p.  75. 

Conversation  7. 

30.  Two  fluids,  one  a  saturated  solution  of  muriate  of  lime,  the  other  a 
similar  solution  of  sulphate  of  soda,  on  being  mixed  together,  become  solid, 
and  heat  is  disengaged.     See  p.  76. 

31.  A  solution  of  Glauber's  salt  saturated  and  corked  up  whilst  at  a  boil- 
ing heat,  will  remain  fluid  when  cold,  until  the  stopper  is  removed,  when 
it  will  instantaneously  crystallize,  and  give  out  heat.     See  p.  76. 

32.  Water  may  be  converted  into  ice  by  evaporation  from  itself  under 
the  receiver  of  an  air  pump.     See  p.  79. 

33.  In  the  palm,  or  boiling"  glass,  water,  or  alcohol,  may  be  made  to  boil 
by  the  heat  of  the  hand.     See  p.  79. 

34.  Water  may  be  frozen,  by  evaporation  from  itself,  in  the  cryophoru* 
invented  by  Dr  Wollaston.     See  p.  80. 

35.  Water  may  be  frozen  by  exposing  it  to  the  influence  of  a  solution 
of  three  different  salts.     See  p.  80. 

Conversation  9. 

36.  A.  peculiar  taste,  andajtfasA  of  light,  maybe  produced  by  the  contact 
of  two  metals,  placed  in  the  mouth.     See  p.  96.  . 

37.  Wires  may  be  made  to  revolve  by  the  combined  action  of  electricity 
and  magnetism.     See  p.  105. 

38.  A  similar  effect  may  be  produced  by  heat  and  magnetism  combined. 
See  p.  106. 

Conversation  10. 

39.  The  air  of  the  atmosphere  is  decomposed  by  a  candle  or  other  body 
being  allowed  to  burn  in  it.     See  p.  108. 

;".'-..  •*s* 

,^r--'^-:- 


INDEX  TO  THE  EXPERIMENTS.  321 


Conversation  11. 

40.  A  candle  just  blown  out,  may  be  relighted  by  putting  it  into  ajar  of 
Oxygen  gas.     See  p.  114. 

41.  Iron  -wire  burns  very  splendidly  in  oxygen  gas,  and  will  be  increased 
in  weight  by  the  combustion.      See  p.  114. 

42.  Sulphur  -when  burnt  in  oxygen  assumes  the  gaseous  form,  and  is  con- 
verted into  an  acid.      See  p.  116. 

43.  A  blue  vegetable  infusion  will  become  red  if  a  minute  portion  of  an 
acid  is  added  to  it.      See  p.  118. 

44.  A  piece  of  potassium  dropped  into  water,  will  immediately  take  fire, 
and  burn  with  great  rapidity.     See  p.  119. 

45.  A  blue  vegetable  infusion  will  be  rendered  green  by  the  addition 
of  an  alkali. 

Conversation  12. 

46.  By  passing  the  vapour  of  water  over  heated  iron,  the  iron  is  oxidized, 
and  hydrogen  gas  (inflammable  air)  produced.      See  p.  123. 

47.  Water  may  be  decomposed  by  the  voltaic  trough.     See  p.  124. 

48.  By   an  apparatus  properly  arranged,  the  two  gases  produced  by  its 
decomposition  may  be  separately  collected.     See  p.  125. 

49.  Water  may  be  decomposed,  and  hydrogen  gas  obtained,by  the  agency 
of  iron  and  sulphuric  acid.     See  p.  126. 

50.  Hydrogen  gas,   issuing  from   a  tube,  will   burn  -with  flame.     See 
p.  128. 

51.  Hydrogen  will  escape  rapidly  from  an  open  vessel,   with  its  mouth 
upwards,  but  if  the  vessel  is  inverted,  it  will  remain  in  it  for  a  considerable 
time.     See  p.  128. 

52.  A  receiver  may  be  filled  with  hydrogen  without  the  use  of  a  pneu- 
matic cistern.      See  p.  129. 

53.  A  candle  may  be  repeatedly  extinguished  and  relighted  by  means  of 
a  phial  filled  with  hydrogen  gas.     See  p.  129. 

54.  If  hydrogen  is  mixed  -with  atmospheric  air,  it  will  explode  when  ig- 
nited.   See  p.  130. 

55.  If  hydrogen  is  burnt  under  a  cold  receiver,  the  ivater  formed  by  the 
combustion  will  be  condensed  within  it.     See  p.  131. 

56.  Musical  sounds  may  be  produced  by  surrounding  a  burning  jet  of 
hydrogen. by  a  tube.     See  p.  132. 

57.  Soap  bubbles  filled  ivith  hydrogen  gas  ascend  rapidly  in  the  atmos- 
phere.    See  p.  133. 

58.  If  filled  -with  a  mixture  of  oxygen  and  hydrogen,  and  a  taper  be  ap- 
plied to  them,  they  will  explode  with  a  loud  report.     See  p.  134. 

Conversation  13. 

59.  Sulphur  may  be  sublimed,  and  converted  into  flowers  of  sulphur,  by 
the  agency  of  heat.      See  p.  136. 

60.  Sulphurous  acid  is  produced  by  the   combustion  of  sulphur  in  at- 
mospheric air.     See  p.  137. 

61.  A  red  rose  may  be  bleached  by  the  vapour  of  burning  sulphur.     See 
p.  139. 

Conversation  14. 

62.  Phosphorus  burns  with  great  splendor  in  oxygen  gas.     See  p.  143. 

63.  Words  written,    or  subjects  drawn  -with  phosphorus,   will  appear 
luminous  in  the  dark.     See  p.  144. 

64.  By  dropping  phosphuret  of  lime  into  water,  phosphuretted  hydrogen 
will  be  produced,  which  will  take  fire  spontaneously.     See  p.  146. 

65.  The  same  gas  may  be  procured  by  the  action  of  caustic  potash  and 


322  INDEX  TO  THE  EXPERIMENTS. 

* 

phosphorus  upon  water;  and  curious  rings  of  vapour  will  be  formed  by  the 
combustion  of  the  gas.     See  p.  147. 

66.  A  solution  of  phosphorus  in  olive  oil  may  be  made  by  carefully  rub- 
bing the  former  with  a  little  of  the  latter,  in  a  mortar,   and  then  adding 
more  oil.      This  fluid,  if  kept  in  a  bottle  partially  filled  with  it  and  closely 
stopped,  will  exhibit  a  luminous  appearance  whenever  the  cork  is  with- 
drawn.    See  p.  147. 

67.  A.  fountain  of  fire  may  be  produced  by  mixing  some  phosphorus  with 
the  materials  for  producing  hydrogen  gas.     See  p.  148. 

68.  Phosphorus  burnt  in  a  given  portion  of  atmospheric  air,  will  de- 
prive it  of  its  oxygen,   and  enable  us  to   discover  how  much  it  contained. 
See  p.  149. 

69.  The  same  fact  may  be  ascertained  by  the  agency  of  hydrogen  gas. 
See  p.  149. 

Conversation  15. 

70.  Fixed  air  (carbonic  acid)  is  produced  by  the  burning  of  charcoal  in 
oxygen  gas.     See  p.  155. 

71.  Water  may  be  impregnated  with  carbonic  aczWby  means  of  Nooth's 
apparatus.     See  p.  157. 

72.  Carbonic  acid  is  much  heavier  than  atmospheric  air,  and  may  be  col- 
lected in  an  open  vessel  by  very  simple  means.     See  p.  157. 

73.  Carbonic  acid  may  be  poured  from  one  vessel  into   another,   like  a 
liquid.      Seep.  158. 

74.  This  gas  may  be  agitated  in  an  open  vessel,  like  water,  and  the 
waves  produced  distinctly  exhibited.      See  p.  158. 

75.  Carburetted  hydrogen,  an  inflammable  gas,  may  be  collected  from 
the  mud  of  ponds,  or  other  waters  nearly  stagnant.      See  p.  161. 

76.  Heavy  carburetted  hydrogen  which  burns  brilliantly,   and  a   large 
quantity  of  charcoal,  may  be  obtained  from  alcohol.     See  p.  162. 

77.  Flame  will  not  pass  through  the  meshes  of  fine  wire  gauze.     See 
p.  163. 

•    Conversation  16. 

78.  Jlmmonia  may  be  disengaged  from  sal  ammoniac,  and  collected  in  the 
gaseous  form  in  an  open  vessel.     See  p.  169. 

79.  On  mixing  two  gases,  carbonic  acid  and  ammonia,  they  will  combine 
and  form  a  solid  substance,  carbonate  of  ammonia.     See  p.  171. 

Conversation  17. 

80.  The  breath  contains  carbonic  acid,  and  will  precipitate  the  lime  from 
lime-water.     See  p.  174. 

81.  Carbonic  acid  will  precipitate  lime  from  water,   and  redissolve  the 
precipitate.     See  p.  174. 

Conversation  18. 

82.  The  reduction  of  a  metal  may  be  exhibited  by  heating  red  lead, 
mixed  with  pulverized  charcoal,  in  a  tobacco  pipe.     See  p.  184. 

83.  The  same  may  be  shown  by  burning  a  common  wafer.     See  p.  184. 

84.  An  alloy  formed  of  bismuth,  tin,  and  lead,  may  be  fused  upon  paper, 
over  a  candle,  without  scorching  the  paper.     See  p.  187. 

85.  By  the  oxy-hydrogen  blowpipe,  the  metals,  in  general,  may  be  burnt 
and  volatilized.     See  p.  190. 

86.  A  mixture  of  filings  of  copper,  or  filings  of  iron,  and  sulphur,  heated 
in  a  flask  over  a  lamp,   will  combine,  and  light  and  heat  will  be  emitted, 
although  no  oxygen  gas  is  present.     See  p.  191. 


INDEX  TO  THE  EXPERIMENTS.  323 


Conversation  19. 

87.  Neither  nitric  nor  muriatic  acid  will  dissolve  gold,  but  when  the  two 
are  poured  together,  its  solution  is  immediately  effected.     See  p.  194. 

88.  If  a  stream  of  hydrogen  gas  be  made  to  blow  upon  spongy  platinum, 
the  metal  will  become  ignited,   this  will  inflame  the  gas,  which  in  its  turn 
will  light  a  taper.      See  p.  196. 

89.  Writing,  or  drawing,  executed  with  a  solution  of  nitrate  of  silver, 
Upon  linen,  prepared  by  an  alkaline  solution,  will  produce  indelible  lines* 
This  is  the  permanent  marking  ink.     See  p.  197. 

Conversation  20. 

90.  By  means  of  the  voltaic  battery  the  alkali  and  acid  contained  in  a 
neutral  salt  may  be  separated  from  each  other.      See  p.  205. 

91.  By  the  agency  of  electricity  an  acid  may  be  made  to  pass  through  an 
alkali,  without  uniting  with  it.      See  p.  205. 

92.  Sal   ammoniac  and  quicklime  are  inodorous,  but  when  rubbed  to- 
gether in  a  mortar,  &  powerful  odour,  that  of  ammonia,  will  be   produced. 
See  p.  206. 

93.  If  four  parts  of  sulphuric  acid  be  mixed  with  one  part  of  water,  both 
cold,   their  combination  will  produce  a  heat  of  upwards  of  300°.      See 
p.  207. 

Conversation  21. 

94.  If  strong  nitric  acid  be  poured  upon  pulverized,  fresh  burnt,  charcoal, 
a  vivid  inflammation  will  be  produced.      See  p.  219. 

95.  Nitric  acid  poured  upon  warm  spirits  of  turpentine,  will  cause  it  to 
burst  into  a  fame.     See  p.  219. 

96.  If  colourless  nitric  acid  be  exposed  to  the  action  of  light,  this  agent 
•will  produce  decomposition,  and  the  acid  will  become  coloured.     See  p.  219. 

Conversation  22. 

97.  If  nitrous  gas,  which  is  colourless,  be  suffered  to  escape  into  the  at- 
mosphere, it  will  assume  a  deep  orange  red  colour,  and  nitrous  acid  vapouf 
•vill  be  produced.      See  p.  222. 

98.  If  pulverized  charcoal,  or  sulphur,  be  mixed  with  nitre,  and  projected, 
in  small  portions,  into  a  red-hot  crucible,  a  vivid  combustion  will  take  place, 
affording  an  example  of  deflagration.     See  p.  228. 

99.  A   mixture  of  nitre,    salt  of  tartar,  and   sulphur,  forms  fulminating 
poivder.     A  few  grains  of  it  heated  over  the  fire  explode  with  a  very  loud 
report.     See  p.  229. 

100.  A  few  grains  of  pulverized  nitrate  of  copper,  wrapped  dexterously 
in  tin  foil,  after  being  moistened,  will  cause  the  foil  to  ignite  and  emit 
sparks.     See  p.  230. 

Conversation  23. 

101.  If  prussiate  ofpotassa,  which  is  colourless,  be  dropped  into  a  solu- 
tion of  sulphate  of  iron,  an  intense  blue  colour  will  be  produced,  in  conse- 
quence of  the  formation  of  Prussian  blue.      See  p.  232. 

102.  Boracic  acid  dissolved  in  alcohol,  will  cause  its  flame  to  assume  a 
beautiful  green  colour.     See  p.  233. 

103.  The  vapour  of  fluoric  acid  may  be  used  for  etching  upon  glass,  by 
a  very  easy  process.     See  p.  234. 

104.  Fluo-silicic  acid  gas,  in  being  absorbed  by  water,  will  deposite 
upon  its  surface  a  perfect  coat,  or  pane,  of  silex.      See  p.  234. 

105.  Various  metals  in  thin  leaves,  or  fine  filings,  will  inflame  and  bum 
spontaneously  in  chlorine;  so  also  will  phosphorus.     See  p.  238. 


324  INDEX  TO  THE  EXPERIMENTS. 

106.  A  red  rose,  pieces  of  printed  calico,  and  various  other  articles,  lose 
their  colour  by  immersion  in  chlorine.      See  p.  238. 

107.  If  hydrogen  and  chlorine  be  mixed  together,  and  inflamed  by  the 
electric  spark,  an  explosion  will  be  produced,  and  muriatic  acid  will  be 
formed.     See  p.  240. 

108.  The  direct  action  of  the  solar  ray  will  produce  an  explosion  in  a 
mixture  of  chlorine  tind  hydrogen.     See  p.  240. 

•';>"..  ..... 

Conversation  24. 

109.  If  a  receiver  filled  with  chlorine  be  allowed  to  stand  over  a  solution 
of  muriate  of  ammonia,  chloride  of  nitrogen  will  be  formed;  a  compound 
which  explodes  ivith  great  violence.     See  p.  243. 

1 10.  A  few  grains  of  loaf  sugar,  mixed  with  half  the  quantity  of  chlorate 
ofpotassa,  will  inflame  if  touched  by  sulphuric  acid.     See  p.  244. 

111.  Matches  first  dipped  in  sulphur,  and  afterwards  in  a  mixture  of 
chlorate  of  potassa,  loaf  sugar,  and  sulphur,  with  a  little  gum  water,  -anil 
in/lame  if  dipped  into  a  phial  containing  sulphuric  acid.    Asbestos  is  put 
into  the  phial,  as  cotton  is  often  used  in  inkstands.     See  p.  245. 

112.  If  phosphorus,  cut  into  small  pieces,  be  put  into  a  glass  with  some 
chlorate  ofpotassa,  and  the  glass  be  filled  with  water,  on  pouring  sulphuric 
acid  so  as  to  run  down  the  inside  of  the  glass,  and  come  in  contact  with  ths 
salt,  the  phosphorus  will  be  in/lamed  under  -water.     See  p.  245. 

113.  If  chlorate  ofpotassa  and  sulphur  be  rubbed  together  in  a  mortar, 
a  series  of  explosions,  like  the  reports  of  pistols,   will  be  produced.     Seei 
p.  245. 

114.  If  sulphur,  or  the  filings  of  a  metal,  be  mixed  with  the  chlorate,  a 
blow  will  cause  the  mixture  to  explode  -with  a  loud  noise.     See  p.  245. 

115.  If  muriatic  acid  and  ammonia,  both  in  the  gaseous  state,  be  brought- 
into  contact  with  each  other,  they  will  combine  and  form  a  solid  salt,  thej 
muriate  of  ammonia.     See  p.  248. 

116.  If  a  leafofgoldbe  put  into  nitric  acid,  and  another  into  muriatic  acid, 
they  will  remain  undissolved,  but  upon  pouring  the  two  together  sofofc'onj 
•will  be  immediately  effected.     See  p.  250. 

117.  If  a  few  grains  of  iodine  are  heated  in  a  closed  glass  retort,  or  re*, 
eeiver,  a  beautiful  violet  coloured  gas  will  be  produced.     See  p.  252. 

Conversations  25,  28,  and  30. 

118.  If  equal  parts  of  crystallized  sulphate  of  soda  and  nitrate  of  ammo 
nia  are  rubbed  together  in  a  mortar,  the  tivo  solid  salts  will  be  converts 
into  a  fluid.     See  p.  256. 

119.  If  sulphate  of  copper  and  nitrate  of  potassa  be  dissolved  together  1 
hot  water,  the  two  salts  will  crystallize  separately  on  allowing  the  solutio 
to  become  cold.     See  p.  257. 

120.  If  a  solution  of  gall  nuts,  and  a  solution  of  sulphate  of  iron,  hot 
nearly  colourless,  be  mixed  together,  they  will  become  intensely  blue,  ap« 
proaching  to  black.    This  is  an  example  of  Reformation  of  ink.    See  p.  285 

121.  If  a  coil  of  platina  wire  be  heated,  and  then  held  over  alcohol  o 
ether,  at  a  little  distance  from  the  surface  of  the  liquid,  the  wire  will  be 
come,  and  continue,  of  a  glowing  red  colour,  occasioned  by  the  combustio 
of  the  vapour.     The  aphlogistic  lamp,  p.  297,  shows  this  effect  in  a  ver 
pleasing  manner. 

122.  If  a  solution  of  gelatine  (common  glue)  be  mixed  with  a  solution  c 
gall  nuts,  or  of  oak  bark,  a  copious  precipitation  will  take  place.     This 
an  example  of  the  formation  of  leather.     See  p.  302. 


325 


INDEX. 


Absorbent  vessels,  306 
Absorption  of  caloric,  77 
Acetate  of  lead,  201 

copper,  200 
Acetic  acid,  297 
Acetous  fermentation,  297 
Acidifying  principle,  111,  141 
Acids,  116 
Adipocire,  304 
Aeriform,  44,  57,  107 
Affinity,  18,  20,  204 
Air-holder,  189 
Air  and  gas,  107 

pump,  water  frozen  by,  60,  79 
balloons,  128,  132 
Albumen,  300 
Alchemists,  14 
Alcohol,  or  spirit  of  wine,  62,  296 

decomposition  of,  161 
Alembic,  62,  161 
Alkalies,  116,118,  165 

vegetable,  283,  285 
Alkaline  earths,  165,  172 
Alloys,  186 

fusible,  187 
Alum,  or  sulphate  of  alumine,   179, 

258 

Alumina,  or  alumine,  179 
Aluminum,  180 
Amalgam,  194 
Amber,  288 

Ammonia,  or  volatile  alkali,  168 
Analogy,  17 
Analysis,  17 

of  vegetables,  282 
Anhydrous  salts,  255 
Animal  matter,  constituents  of,  279 
acids,  302 
heat,  311 
oils  and  fats,  303 
chemistry,  299 
Anthracite,  289 
Antimony,  203 
Aphlogistic  lamp,  297 
Aquafortis,  22,  218 
Aqua  regia,  194,  250        \ 
2  C 


Arrow  root,  292 
Argil,  179 
Arsenic,  202 

and  arsenious  acids,  202 
Arteries,  308 
Arterial  blood,  308 
Asphaltum,  289 
Astringent  principle,  293 
Atmosphere,  106,  158 

its  pressure  influences 
the  boiling  point,  56, 
61 
Atomic  theory,  211 

weights,  212,  226 

Attraction  of  aggregation,  or  cohe- 
sion, 18 

Attraction  of  composition,  18,  20 
Azote,  or  nitrogen,  107, 121 

Balloons,  air,  132 

Barium,  176 

Bark,  301 

Barometer,  59 

Baryta,  or  baryteSj,  175 

Bases,  107 

Base  of  acids,  117 

gases,  107,  110 

salts,  120,  154 
Basis,  or  mordant,  294 
Bell  metal,  186 
Bile,  307 
Bismuth,  302 
Bitumens,  289 

Black  lead,  or  plumbago,  199 
Bleaching,  138,  238,  249 
Blende,  202 

Blowpipe,  oxyhydrogen,  188,  191 
Blood,  306 
Bloodvessels,  308 
Boiling  point,  47,  73 

water,  55 

in  vacuo,  57 

point  of  different  fluids,  50 

glass,  79 
Bones,  142 
Boracic  acid,  232 


326 


INDEX. 


Boron,  233 

Borate  of  soda,  or  borax,  232 

Brandy,  63 

Brass,  186 

Bromine,  252* 

Bread,  292,  298 

Bricks,  179 

Bronze,  200 

Bubbles,  soap,  filled  with  hydrogen, 

133 

Burning  glass,  86 
Buttermilk,  305 

Calamine,  202 

Calcareous  earths,  175 

Calcined  magnesia,  176 

Calcium,  175 

Calomel,  25 

Caloric,  27 

absorption  of,  42 
conductors  of,  30,  33 
combined,  27,  28,  65 
expansive  power  of,  43, 45, 48 
equilibrium  of,  28 
reflection  of,  42 
radiation  of,  29,  36 
solvent  power  of,  58,  81 
capacity  for,  65,  71 
specific,  67,  70 
of  fluidity,  72 

Calorimotor,  103 

Camphor,  287 

Caoutchouc,  288 

Capacity,  heat  of,  71 

Carbonates,  156 

Carbonate  of  ammonia,  171 
lead,  201 
lime,  156,  173 
magnesia,  176 
potassa,  166 

Carburetted  hydrogen  gas,  159 

Carbon,  150 

Carbonic  acid,  154 
oxide,  159 

Carburet  of  iron,  199 

Caseous  matter,  or  curd,  304 

Caustic,  167 

Cementation,  199 

Ceruse,  201 

Chalk,  156,  173 

Charcoal,  150 

indestructibility  of,   153 

Cheese,  305 

Chemical  attraction,  18,  20,  204 
miracle,  76,  256 

Chemistry,  15 

China,  177,  179 


Chlorate  of  potassa,  243. 

Chloric  acid,  242 

Chloride  of  nitrogen,  243 
sodium,  246 
lime,  249 
mercury,  251 

Chlorine,  237 

Chloriodic  acid,  252 

Chromate  of  iron,  202 

Chrome,  181,  203 

Chromic  yellow,  203 

Chyle,  306 

Chyme,  306 

Cinchonia,  285 

Cinnabar,  197 

Citric  acid,  284 

Circulation  of  the  blood,  308 

Clay,  179 

Clouds,  84 

Coke,  289 

Copal,  287 

Coal,  289 

Corrosive  sublimate,  251 

Cobalt,  200,  203 

Cold,  31,  85 

from  evaporation,  61 
apparent  radiation  of,  39 

Colours,  adjective  and   substantive, 

294 
of  metallic  oxides,  120 

Colour  influences  radiation,  41 

Colouring  matter,  293 

Columbium,  202 

Combined  caloric,  28,  70 

Combustion,  107,  109 

volatile  products  of,  110 
fixed  products  of,  110 
of  alcohol,  296 
by   oxymuriatic     acid, 

or  chlorine,  238 
of  carbon,  154 
of  charcoal,    by   nitric 

acid,  219 

of  candles,  108,  114,160 
of  diamonds,  155 
of  ether,  38 
of  hydrogen,  128,  131 
of  iron,  114 
of  metals,  188 
of  metals  by  chlorine, 

238 
of  oil  of  turpentine,  by 

nitric  acid,  219 
of  phosphorug,  143 
of  sulphur,  116,  137 
of  potassium,  119 
supporters  of,  109 


INDEX. 


327 


Combustion,  spontaneous,  286 
in  chlorine,  238 
of  metals  by  chlorate  of 

potassa,  245 
Compound  bodies,  17 
Condensation  producing  heat,  69 

of  steam,  73 
Conductors  of  heat,  30 

solid,  31,  33 
fluid,  32,  34 
Count  Rumford's 

theory  of,  34 
Constituent  parts,  16 
Copper,  200 
Copperas,  20,  139 
Copal,  287 

Couronnedestasses,  98 
Cream,  304 
Crassamentum,  309 
Cream   of  tartar,    or   bitartrate   of 

potash,  284 
Crucibles,  228 
Cryophorus,  80 
Crystals,  258 
Crystallization,  76,  256 
Crystallography,  259 
Curd,  or  caseous  matter,  304 
Cyanic  acid,  232 
Cyanogen,  231 

Davy's  safety  lamp,  162 

Decomposition,  16 

of  atmospherical  air, 

108,  148 
of  salts,  by  the  voltaic 

battery,  204,  205 
of  water  by  metals, 

123,  185 

of  water    by  potas- 
sium, 119 

of  water,  by  the  vol- 
taic battery,  124 
of  vegetables,  282 
of  potash,  118 
of  soda,  118 
of  ammonia,  170 
of  boracie  acid,  232 
of  muriatic  acid,  235 

Deflagration,  228 

Definite  proportions,  210 

Derbyshire  spar,  233 

Deliquescence,  254 

Dephlogisticated  air,  111 

Detonation,  229 

Dew,  82 

Diamond,  151 

Digestion,  307 


Dissolution  of  metals,  101,  184 
Distillation,  62 

destructive,  281 
Double  elective  attraction,  208 

salts,  258 
Drying  oils,  286 
Ductility,  187 
Dyeing,  294 

Earths,  172 
Earthenware,  177,  179 
Efflorescence,  254 
Elaine,  303 
Elastic  fluids,  44,  57 
Electricity,  86 

voltaic,  95 
by  induction,  91 
Electric,  or  Leyden  jar,  90,  93 
Electric  machine,  89 
Electro-positive  bodies,  101 
Electro-negative  bodies,  101 
Electro-magnetism,  104 
Elective  attraction,  22 
Elementary  bodies,  16 
Enamel,  178 
Epsom  salt,  177 
Equilibrium  of  caloric,  28,  81 
Equivalents,  226 
Essences,  287 
Essential,  or  volatile  oils,  286 

salt  of  lemons,  283 
Etching  on  glass,  234 
Ether,  296 

water  frozen  by  its  evapora- 
tion, 60,  77 
Evaporation,  54,  78 
Euchlorine,  242 
Eudiometry,  148 
Eudiometers,  149 
Exhilarating  gas,  224 
Expansion  by  caloric,  43 

of  solids,  44 

of  liquids,  45     . 

of  gases,  48 

Falling  stones,  180 

Fats  and  oils,  303 

Fecula,  292 

Fermentation,  294 

Ferrocyanate   of  iron,    or  Prussian 

blue,  231 
Fibrin,  299 
Fire,  16 
Fish  glue,  301 
Fixed  air,  or  carbonic  acid,  154 

alkalies,  165 

oils,  286 


328 


INDEX. 


Fixed  products  of  combustion,  110 

Flame,  160,  162 

Flint,  177 

Fluidity,  53,  72 

Fluoric  acid,  233 

Fluate  of  lime,  233 

Fluosilicic  acid  gas,  234 

Fluorine,  235 

Fluxes,  184 

Fog,  84 

Forms  of  bodies,  43 

Fountain  of  fire,  148 

Free  caloric,  or  heat  oi  temperature, 

28 
Freezing  mixtures,  75,  80,  315 

point,  47 

water  by  evaporation,  78 

ether,  60 
Fulminating  powder,  229 

silver,  197 
Fulminic  acid,  197 
Fui-nace,  123 
Fusible  alloy,  187 
Fusion,  43,  52 

of  the  pure  earths,  190 

Galena,  201 
Gall  nuts,  285 
Gallate  of  iron,  285 
Gallic  acid,  284 
Galvanism,  95 
Galvanic  pile,  96 

battery,  97,  98 
Gas,  107 

simple,  107 

Gases  penetrate  membranes,  310 
Gas-lights,  160 

Gases  absorbed  by  charcoal,  154 
combine  by  volumes,  212 
Gaseous  oxide  of  carbon,  159 
Gas-holder,  189 
Gastric  juice,  307 
Gelatine,  or  jelly,  300 
Gilding,  194 
Gin,  63 
Glands,  306 
Glass,  168,  178 
Glauber's  salt,  or  sulphate  of  soda, 

235 

Glazing,  179 
Gliadine,  292 
Glucine,  180 
Glue,  301 
Gluten,  292 
Glycerine,  303 
Gold,  193 
Gum,  291 

elastic,  or  caoutchouc,  288 


Gum  resins,  288 
Gunpowder,  229 

Gypsum,  plaster  of  Paris,  or  sulphate 
of  lime,  175 

Hailv84 

Hare's  blowpipe,  188 

Harrowgate  water,  140 

Hartshorn,  169 

Heart,  310 

Heat,  27 

of  capacity,  65,  71 

free,  28 
•  latent,  28,  70 

radiant,  28 

sources  of,  28 

specific,  67,  70 

passes  through  transparent  me- 
dia, 85 

from  combustion,  109 
Honey,  291 
Horns,  300 
Hydracids,  231 
Hydrates,  255 

Hydrocarburet  of  chlorine,  243 
Hydrogen,  121 

gas,  122, 126 
Hydrofluoric  acid,  235 
Hydrocyanic  acid,  231 
Hydrosulphuric  acid,  141 
Hydrosulphurets,  142 
Hydrochloric  acid,  242 
Hydriodic  acid,  251 
Hyponitrous  acid,  224 

Ice,  60,  71,  74,  78 

Ichthyocolla,  301 

Jelly,  or  gelatine,  300 

Ignis  fatuus,  144 

Ignition,  or  incandescence,  43,  64 

Imponderable  agents,  23 

Incompatible  salts,  256 

Inflammable  air,  122 

Inflammables,  simple,  135 

Ink,  285 

Integrant  parts,  16 

particles,  262 
Iodine,  251 
lodic  acid,  252 
Jridium,  196 
Iron,  198 

meteoric,  198 
Isinglass,  or  ichthyocolla,  301 

Lac,  287 

Lacteals,  306 

Lakes,  294 

Lamp  without  flame,  297 


INDEX. 


Latent  heat,  28,  70 

Lead,  200 

Leather,  302 

Life,  279 

Lignin,  293 

Light,  24 

from  combustion,  109 
and  heat  separable,  24,  39 
chemical  effects  of,  25 

Lightning,  87,  94 

Lime,  77,  173 

Lime-water,  173 
stone,  173 

Linseed  oil,  286 

Liquefaction,  43,  52 

of  gases,  107 

Lithia,  166 

Litharge,  201 

Loadstone,  200 

Lunar  caustic,  or  nitrate  of  silver,  196 

Lungs,  310 

Magnetic  needle,  200 

Magnesia,  176 

Magnesium,  177 

Malic  acid,  284 

Malt,  292 

Malleability,  187 

Malleable  metals,  1 87 

Manganese,  111,  186 

Manna,  291 

Manure,  175 

Marble,  156 

Margaric  acid,  303 

Marine  acid,  or  muriatic  acid,  235 

Marking  ink,  197 

Mastic,  287 

Match  lights,  245 

Mercury,  77,  173,  197 

forms  amalgams,  194 
Metallic  acids,  202 

oxides,  116,  186 

salts,  185 
Metals,  181,  192 

date  of  their  discovery,  193 
their  distinguishing  proper- 
ties, 182 

Meteorology,  84 
Meteoric  stones,  180 
Milk,  304 
Mineralizer,  183 
Mineral  waters,  134 
Minium,  201 
Miners'  lamp,  162 
Miracle,  chemical,  76,  256 
Molybdenum,  202 
Mordant,  or  basis,  294 
Morphia,  285 

2  C  2 


Mortar,  174 

Mucilage,  291 

Muriatic  acid,  or  marine  acid,  235 

Muriate  of  ammonia,  169,  247 

lime,  76,  248 

soda,  or  common  salt,  235, 
246 

magnesia,  247 

Musical  tones  by  hydrogen,  132 
Muscles  of  animals,  300 

Naphtha,  164,  289 

Narcotine,  285 

Natural  philosophy,  14,  15 

Nascent  state  of  a  gas,  145 

Negative  electricity,  83 

Neutralization,  119 

Neutral  salts,  119 

Nickel,  181,  200 

Nitre,  nitrate  of  potash,  or  saltpetre, 

20,  227 
Nitric  acid,  22,  217 

oxide,  216,  221 
Nitrogen,  or  azote,  107 
Nitromuriatic  acid,  or   aqua  regia, 

194,  250 
Nitrous  acid  gas,  185,  216,  222 

gas,  or  nitric  oxide,  216,  221 
oxide,  216,  224 
Nitrates,  227 

Nitrate  of  copper,  185,  200,  221 
ammonia,  224 
potash,  nitre,  or  saltpetre, 

20,  227 

silver,  or  lunar  caustic,  196 
lime,  227 
Nomenclature,  117 

of  acids,  117 

of  oxides,  120 

of  salts,  120 

of    double,    or   triple 

salts,  258 

of  wilphurets,  &c.  140 
Nooth's  apparatus,  157 
Noyeau,  231 
Nut-galls,  285 

oil,  286 
Nutrition,  306 

Oils,  fixed  and  volatile,  286 

Oils  and  fats,  animal,  303 

Oil  of  vitriol,  or  sulphuric  acid,  19 

78,  117,  139 
Oleic  acid,  303 
Olefiant  gas,  162,  243 
Olive  oil,  286 
Ores,'  183 
Organized  bodies,  152,  278 


330 


INDEX. 


Organs,  279 

Osmazome,  301 

Osmium,  196 

Oxalic  acid,  121,  284 

Oxides,  116 

Oxide  of  manganese,  111 

iron,  115 

lead,  111 

mercury,  111 
Oxidation,  116 

of  metals,  184 
Oxygen,  100,  107,  111,  227,  244 

a  constituent  of  water,  122 
Oxyhydrogen  blowpipe,  188,  191 
Oxymuriatic  acid,  238 
Oxymuriate  of  potassa,  243 

Palladium,  196 

Palm  glass,  79 

Panary  fermentation,  298 

Particles,  19 

Pearlash,  167 

Percussion  powder,  246 

Perchloric  acid,  242 

Perfect  metals,  184 

Perfumes,  286 

Peroxide  of  chlorine,  242 

Permanent  salts,  254 

Perspiration,  312 

Petroleum,  289 

Pewter,  186,  201 

Pharmacy,  14 

Philosophical  candle,  128 

Phosphate  of  lime,  142 

Phosphuret  of  lime,  146 

Phosphuretted   hydrogen   gas,    144, 
147 

Phosphorescence,  26 

Phosphoric  acid,  143 

Phosphorus,  111,  142 

dissolved  in  oil,  147 

Phosphorous  acid,  144 

Pitch,  289 

Plaster  of  Paris,  174 

Platinum,  195 

Platina  ignited  by  a  stream  of  hydro- 
gen, 196 

Platina  sponge,  195 

Plumbago,  or  black  lead,  199 

Pneumatic  chemistry,  112 

cistern,  112,  126  . 

Porcelain,  177,  179 

Positive  electricity,  88 

Potassium,  111,  118 

Pottery,  179 

Potassa,  or  potash,  111,  118,  166 

Pulse  glass,  79 

Precipitation,  20 


Pressure  of  the  atmosphere,  56,  61 
Primary  forms  of  crystals,  260 
Protoxide   of  nitrogen,    or   nitrous 

oxide,  216 
Protoxide  of  chlorine,  or  euchlorine, 

242 
Proximate  principles  of  vegetables, 

282 
Prussiate  of  iron,  231 

potash,  232 
Prussic  acid,  231 
Putrefactive  fermentation,  298 
Pyrites,  or  metallic  sulphurets,  182 
Pyrometer,  44 

Wedgwood's,  50 
Pyroligneous  acid,  298 

Quicklime,  77,  173,  197 
Quinine,  285 

Radiation  of  caloric,  29,  36,  82 

Pictet's  experiments  on,  38 
Leslie's  illustrations  of,  40 
influence  of  colour  on,  41 

Rarefaction  of  air,  70,  85 

Rain,  84 

Reagents,  118 

Receiver,  64 

Rectification,63 

Red  precipitate,  198 
lead,  201 

Reduction  of  metals,  183 

Reflection  of  caloric,  42 

Regulus  of  antimony,  203 

Rennet,  305 

Resins,  287 

Respiration,  310 

Retort,  64 

Rhodium,  196 

Roasting  metals,  183 

Rochelle  salts,  284 

Rock-crystal,  177 

Rosin,  287 

Ruby,  180 

Rum,  63 

Rust,  115 

Saccharine  fermentation,  295 

Safety  lamp,  162 

Sal  ammoniac,  or  muriate  of  ammo- 
nia, 169,  247 

Sal  volatile,  or  carbonate  of  ammo- 
nia, 171 

Salifiable  bases,  120 

Sandarach,  287 

Saltpetre,  nitre,  or  nitrate  of  potash, 
20 

Salts,  120,  253 


INDEX. 


331 


Salts  decomposed  by  electricity,  204, 
205 

separation  of,  from  each  other, 

256 

Sand,  177 
Sap  of  plants,  282 
Sapidity  of  salts,  254 
Saponification,  303 
Sapphire,  180 
Saturation,  59 
Seas,  temperature  of,  51 
Secondary  forms  of  crystals,  260 
Secretions,  307 
Selehic  acid,  232 
Selenium,  232 
Selttzer  water,  156 
Sensible  heat,  28 
Serum,  309 
Shells  of  fishes,  174 
Silex,  or  silica,  177 
Silicon,  179 
Silver,  196 

Silvering  looking  glasses,  197 
Simple  affinity,  22 
Simple  bodies,  17 

inflammables,  135 
Size,  301 
Skins,  301 
Slaking  of  lime,  77 
Smalt,  203 
Smelting  metals,  183 
Smoke,  110 
Snow,  84 
Soap,  167,  303 

bubbles,  132 
Soda,  111,  118,  168 

water,  156 
Sodium,  111,  118 
Solar  phosphori,  26 
Soldering,  188 
Solubility  of  salts,  254 
Solution,  57,  257 

by  the  air,  81 

.     of  potash,  119 
Specific  heat,  67 
Speltre,  202 
Spirits,  62,  161 

Spongy  platinum  apparatus,  196 
Spontaneous  decomposition,  280 
Starch,  292 
Stearine,  303 
Stearic  acid,  304 
'Steam,  57,  73 
Steam  engine,  266 

piston  and  cylinder,  268 
stuffing  box,  268 
boiler  and  furnace,  268 
safety  valve,  271 


Steam  engine,  condenser,  269 

atmospheric,  272 
Watt's,  273 
parallel  motion,  276 
high  pressure,  277 
Steel,  199 
Still,  62- 
Stomach,  306 
Stones,  172 

meteoric,  180 
Strontites,  or  strontia,  176] 
Strontium,  176 
Sublimation,  136 
Sugar,  290 

of  milk,  304 

Sulphates,  and  sulphites,  120 
Sulphate  of  alumine,  or  alum,  179, 

258 

Sulphate  of  copper,  19,  200 
iron,  21,  139 
lime,  gypsum,  or  plaster 

of  Paris,  174 
magnesia,  or  Epsom  salt, 

177 
soda,  or  Glauber's  salt, 

76,  235 

zinc,,  or  white  vitriol,  202 
Sulphur,  116,  135 

flowers  of,  136 

Sulphuretted  hydrogen  gas,  140 
Sulphured,  140,  182,  t91 
Sulphuret  of  carbon,  164 
Sulphurous  acid,  117,  138 
Sulphuric  acid,  19,  78, 117,  139 
Synthesis,  17 

Tannin,  293 

Tanning,  301 

Tar,  289 

Tartar  emetic,  or  tartrate  of  antimo- 
ny and  potassa,  284 

Tartaric  acid,  284 

Tartrate  of  potash  and  soda,  258 

Tellurium,  202 

Temperature,  28,  81 

Tests,  or  reagents,  118 

Thaw,  82 

Thermo-magnetism,  106 

Thermometers,  46,  59 

Fahrenheit's,  47 
Reaumur's,  47 
Centigrade,  47 
air,  48 
differential,  49 

Thorina,  172,  180 

Thunder,  87,  94 

Tin,  186,  201 

Titanium,  200 


332 


INDEX. 


Transparent  media,  85 
Triple  salts,  258 
Tungsten,  202 
Turpentine,  287 

oil  or  spirits  of,  287 

Ultimate  atoms, 

analysis,  282 

Vapour,  63,  74 

Vaporization,  54 

Varnishes,  288 

Vegetables,  composition  of,  279 

Vegetable  chemistry,  281 

Vegetable  acids,  283 
colours,  293 
oils,  286 
alkalies,  283,  285 

Veins,  308 

Venous  blood,  308 

Ventricles,  310 

Verdigris,  200 

Vermilion,  197 

Vinegar,  298 

Vinous  fermentation,  295 

Vital  air,  or  oxygen  gas,  111 

Vitrification,  178 

Vitriolic  acid,  or  oil  of  vitriol,  139 

Volatile  substances,  54 
oils,  286 

products  of  combustion,  110 
alkali,  165 

Voltaic  electricity,  or  galvanism,  95 
salts  decomposed 
by,  204 


Voltaic  battery,  97,  98, 124 
pile,  96 

Water,  121 

decomposition  of,  by  electri- 
city, 124,  125 
by  potassium,  119 
by  metals,  123,  126 
of  the  sea,  52 
boiling,  55 
solution  by,  58,  134 
of  crystallization,  255 
greatest  density  of,  51 
frozen  by  evaporation,  60,  78 
composition  of,  synthetically 

proved,  131 
Newton's  conjecture  respect 

ing,  121 
Wax,  288 
Welding,  188 
Whey,  304 
Wine,  62 
Woody  fibre,  293 
Woulfe's  apparatus,  236 

Yeast,  296 
Yttria,  180 

Zaifre,  203 
Zero,  74 
Zinc,  201 
Zircon,  180 
Zymome,  292 


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